No, it is not as rare as you think. At least it is more often than underpromotion to a bishop. Frankly i never sac my Queen unless there is a forced mate, of I get some material in return ( 2 rooks or more). I didn't like to sac it for R+B because the defence later will be much harder (they can't protect each other) while for 2 knights it is foolish (the can protect each other but it's more like freezing each other)
My immortal queen sacrifice

I sacked my queen on at least 10 occasions so far but only in two situations to be frank. Either was the Legall's mate in question or the smothered (Philidors) mate .
I hope one day I'll be able to make a sound positional queen sac. But to do that one needs to know how to play chess for real

Angelo, it is still a sac. Maybe Larsen means it is not a really good one.
As for gabriella, sacing a queen for positional means is extremely difficult. Not only the oppurtunity is rare, also your hand doesn't agree with your brain at that time.
Brain: Come on! You will win by sacing your queen!
Hand: What? I only get two bishops and two pawns for the queen?
Brain: Yes, but your pieces will be more active!
Hand: Active is subjective!
Brain: Just do it!
Hand: No, I can't. *makes another move*
Brain: YOU STUPIDDAFOOL
And it happens lots of time, lol

@ Larsen has sacrificed enough queens and pieces to know what he is talking about.
@williamn27 : I think that to Larsen, you can call it a sacrifice only if it is a positional sacrifice, or at least if the fight is not over as soon as your piece is taken (which is the case here).
Suppose you have a knight pinned to your queen, and your opponent use this pin to move an unprotected piece to a place where it can be taken by the knight : you would not call it a sacrifice I think.

Meh. A two-move mating combo where you're already a couple of pieces up and the opponent has no threats, and he could still have delayed the mate by not taking the queen. Looks extremely "mortal" to me.
Better is 1. ... Qh5 in my opinion, you still have the mate if the opponent takes and you have more threats if he doesn't. Still, can't expect too much depth in a one-minute woodpushing contest.
Round about my first game on this site, I played a real queen sac - and they don't come along very often. Didn't give me a forced mate next move but I got a huge mating attack out of it and my oppo couldn't find any defence other than a counter-sac of his own, which left me with too much material. That was fun.

Well that's great Gil, but, doesn't it help the knight to develop? why not let him capture your Queen rather than capturing the bishop yourself? I'm not very highly rated but I simply to noob to understand.

Well, there are different queen sacrifices. Some are not , some are...
Gil-Gandel, first of all you can't really show queen sacrifice from Daily Chess. This is not real chess. I am sorry. And yes my queen sac was the best move and it leads to checkmate in 8. More over stockfish can't see imidiately the queen sac, you have to give him 5 seconds or so and only then shows my move, where in your case not, but as i said your case does not matter becouse its correspondece chess.
Then your opponent was forced to give away his queen 2 moves after that and game continued 10 more moves and could go even more. In any position when you are up enough in material or position you can just hang your queen and you can still win, that's different type of sacrifice and its very common when you are very ahead on position. For example even versus some players you can sac a queen for a pawn on move 2 and win the game.
In my case i saw a possible mate that my opponent did not. I made a piece combination. 3 piece checkmate with knights and bishop only is rare at non master level and dificult to do. This type of checkmate is impossible for many of you and its very beautifull.

I agree - it was a nice and quite a rare checkmate.
And if Larsen ever said that it's not a sac if there's a forced 2 move mate after the capture - and I haven't seen any quotes - then that is absolute rubbish.
My definition of a sacrifice is to give a piece away that hopefully IMPROVES your position. One could give numerous examples, for instance, you may have a terrible position, you play a sac, it's accepted, and now your game is still bad, but you've slightly improved it.
In Angelo's diagram, of course that's a sacrifice, because White's position will improve IF Black accepts it and takes the Bishop, as he'll lose his Queen and have the worse game.
In AIM-AceMove's case. it's irrelevant that he's more that 2 Bishops ahead, he sacs his Queen and improves his position after acceptance by mating in 2. If the sac isn't accepted, he's still improved because he's won a pawn and now has numerous discovered checks added to the Knight checks and the Queen threats.

He only had a forced mate in 2 because of the sacrifice, and he's not guaranteed a win or any result until the game is over - he might fall into traps, blunder some pieces and lose.
Well that's great Gil, but, doesn't it help the knight to develop? why not let him capture your Queen rather than capturing the bishop yourself? I'm not very highly rated but I simply to noob to understand.
The opponent might just refuse to take the queen. Also the knight is not "developed" on a3, it is hanging under attack.

Well, there are different queen sacrifices. Some are not , some are...
Gil-Gandel, first of all you can't really show queen sacrifice from Daily Chess. This is not real chess. I am sorry. And yes my queen sac was the best move and it leads to checkmate in 8. More over stockfish can't see imidiately the queen sac, you have to give him 5 seconds or so and only then shows my move, where in your case not, but as i said your case does not matter becouse its correspondece chess.
lol. Whatevs. Correspondence doesn't count but your blitz combo is deep, sound and amazingly clever. Sure.

Well that's great Gil, but, doesn't it help the knight to develop? why not let him capture your Queen rather than capturing the bishop yourself? I'm not very highly rated but I simply to noob to understand.
The knight's a liability after 16. ... gxf3 as if White plays 17. Qxf3 I have three pieces for the Queen and White's King is still in trouble - I figured this was a position where the three pieces are easily beating the Queen. So White has to use a tempo to save the Knight and then the attack down the h-file is enormous. AIM-AceMove can probably explain why 19. Nxf3 doesn't save White but I'd like to see him do it without Stockfish which I, for one, have never used.
It's actually quite a challenge to explain my reasoning from a game I played six years ago but I thought it was sound at the time.
Also notice that when White plays 21. Rfe1 he's not just dropping a piece for nothing. The Knight is stuck because of the mating threats. If he flees to, say, d2 (21. Nd2) then 21. ... Ne2+ and mate next move, while if 21. Nh2 then 21. ... Nh3# (a nice minor piece mate for the OP to enjoy), or 21. Nh4, Rh8! and the Knight has to be dropped after all because of the mate on h1 if he moves (or 22. Ng2, Ne2# again).
Footnote: The ratings on that game were by no means current at the time - I was rated *much* lower than that!

He only had a forced mate in 2 because of the sacrifice, and he's not guaranteed a win or any result until the game is over - he might fall into traps, blunder some pieces and lose.
Yes, and you might as well finish off a game you're already winning as quickly as possible, even if it's a weaker player (as the OP explained). But it takes more than that to make an "immortal" Queen sacrifice, and disrespecting your opponent by saying he "played quickly and carelessly and thats what happened to him. He imidiately run away with big shame on him" is not at all classy. (My oppo in the game cited was a real gent and it was a pleasure to play him.)

Ofcourse is not deeply planned and game was a blitz 5+5 game if i remember. Is not official game or very importhan for me ~ anything like that. Immortal might be too strong word, becouse they use it for classical games that everyone remembers etc. But still is rare and extraordinary and pretty. And most importhan far better than any long planned or crazy whatever Daily chess example for reasons already stated.
As GM Simon Williams says somtimes for his simular blitz combos.. a combination/game suitable for putting it in your grave stone :D Not sure about mine, but for sure it deserve a place here :D
I always hated queen sacrifices. I never liked them, becouse i hardly see them in real game and i don't like giving my queen just like that. I failed many tactics from tactic trainer. I see a win, i see big advantage but puzzle failed, why... becouse i did not sacrificed my queen..
Also those big sacs like giving away queen are somewhat rare, this one is more unique, becouse there is no pawn or rook, simple piece cordination.
In real games its very dangerous to make those sacs, you can lose very quickly. Thats why i love playing casual, unrated blitz games specially vs little lower rated than me. I just have fun and i am able to do almost whatever i want and to create amazing combinations punishing all that agression and pawn pushers. Opponent below had a lot of time to think but he as many played quickly and carelessly and thats what happened to him. He imidiately run away with big shame on him.