I know this is considered as true due to the asigned and widely accepted individual values of each piece. But I think it's more of a mathematical truth than a practical one. If you ask me I'd rather be on the 2 minor pieces side. I don't think a rook and a pawn can compensate the mobility and combined strenght of 2 pieces that can focus their attack or hit 2 oposite sides of the board at the same time. In adition, rooks have to keep running away from threats by minor pieces since loosing the exchange would be tragic.

I believe the only scenario where the rook and pawn can equalize is in an open board endgame with lots of space. What do you think of this? what's your game experience in this situation?

btw, sorry if this as allready been posted.

I agree. But that would be on an empty board with only this pieces. Just add a few pawns to each side and the strength balance changes drastically... Or so I think.

Just a few notes on this:

A knight and a bishop + the king, are sufficient to mate a lone king. It's lengthy but possible, and most expert-level player and masters should be able to do it.

My ex-coach used a slightly different point values for the pieces; rooks were five and pawns were one (if they were connected to other pawns, and not backward or doubled). But N were 3.1 and bishops 3.3. We fed these values to a computer for auto-play (Chesmasster 6000, I think. It was a while ago) and these values won a "tournament" within the computer's play. So I'd argue that two pieces are better than a rook + pawn.

Of course, each individual position can have its own characteristics. On a board where it's all closed up and only a column is open I'd bet on the rook. If the N is outposted nicely, I think that can be a winning advantage. And so on.

Obviously the situation depends. (Just a side note, a knight and bishop can checkmate contrary to Kupov's beliefs :D)

I would most likely prefer the two minors in the middlegame, where rooks usually don't exert much influence. As the endgame approaches the power of the rook increases, but if my two minors are both bishops I would still prefer that. The rook and pawn only really gains pawer if that power is a dangerous passed pawn. 

I agree, considering the rest of the pieces, I think in the opening two minor pieces are superior. with an empty board the rook and the pawn. 
Besides this you should consider whether it changes positions, whether it costs or wins tempo, and whether there is one player ahead of the other one.
It is hard to answer such general questions that are bound to specific situations.
I think chess is about knowing the right choice in a given situation, so of course the answer isn't simple. So just try it out and see when it does or doesn't work.

ps. I suppose you are implying the knight + bishop for the rook and pawn after the castling rook and a pawn one diagonal in front of it. In my case (personally) I like it when people trade their B and N for my pawn and R, it costs them tempo and opens a half line for my rook. 

It IS possible to checkmate with a knight, bishop and king.  It IS possible to checkmate with 2 knights.  Both are very difficult but possible.

they can checkmate, but they can't force a checkmate

king + bishop + knight vs. a lone king is a forced win for the stronger side.

http://www.chess.com/forum/view/general/checkmate-with-knight-and-bishop
Sorry, you're right. Though I'd be surprised if I managed to

king knight and bishop can force checkmate on lone king as bondiggity said......2 knights cannot force checkmate even with king

The answer to these "what is the worth of such and such piece" is always the same, I think. Generally, the point value system is true, but the actual value can fluctuate wildly based on the position. In some positions, a rook and a pawn would be worth way more than the two pieces, but in others it could easily be the other way around. It just depends.

Rook + 1 Pawn < 2 Minor Pieces
Rook + 1.5 Pawns = 2 Minor Pieces

It all depends.  That's one of the things that makes chess the intriguing game that it is.

There is an excellent article:

"The Evaluation of Material Imbalances" by IM Larry Kaufman:

http://home.comcast.net/~danheisman/Articles/evaluation_of_material_imbalance.htm

Here is an excerpt from it: 

"How about the common situation of rook and pawn(s) vs. two minor pieces? My data shows equilibrium at 1½ pawns (slightly less when both minors are knights), assuming no bishop pair advantage. When the side with the minors has the bishop pair advantage, two pawn makes things about even (slightly better for the rook's side if he has one bishop, slightly worse if he has none)".

very interesting, thanx

Just like any exchange it'll be more favourable to one side or the other, depending on what's left on the board.  There are too many exceptions to make a general rule all that useful.

in mid game, I think two minor pieces (b&K) willhave an advantage over the rook+pawn...

In the endgame, where all the pieces are active, I'd assume Rook and pawn are roughly equal to two minor pieces.

However, in the middle game, I think it's a mistake to trade away two active pieces for an undeveloped Rook and pawn. You lose a lot of tempo, and your opponent's already developed minor pieces may be able to run over your position. 

Here's a game I played some time ago where my oponent chose to trade my castle rook and pawn for 2 minor pieces. It didn't turn out well for him in the long run. I think it's because he shouldn't have traded away his 2 most active pieces.

This game shows no "high level chess" but I guess it belongs to this thread. If you have other games with this kind of trade, please post them for the rest of us to see.

In an earlier post on this thread relating to checkmates, two knights and a king CAN checkmate the opponent, however it CANNOT be forced.