how big is the difference between elo and live rating?

Completely different.

You mean the chess.com rating? I think that your ELO would be about 200 points lower than your rating here. 

My USCF rating was 1800 and I have a helluva time staying 1500 here. 

Of course I like to drink a lot and play here, I also get up at 4AM and start making moves before I'm running on all 8 cylinders. 

As a general rule, USCF + 600 = Live blitz.

So if you're under 1800 live blitz, you're worse than a beginner.

Unlike playing OTB, playing online entails having to deal with players that use less than "reputable" means of playing.

That's a bunch of bull!

It varies from person to person.  There are 1900 players on here that can't even maintain a 1200 OTB rating.

Then there are people like myself and another that posted higher up in the thread where it's almost impossible to get the rating on here as high as our OTB rating.

OTB:  2063 (May 2017)

Here:  Fluctuates between 1850 and 1925.

I was just joking, as in a bunch of other threads. 

3 years ago, on my old account, I had a 2000-2100 bullet rating, 1900-2000 blitz, 1900 daily, right when I got my rating of 2027 OTB. Haven't played in tournaments ever since, although I've practiced a on/off.

It should be actually not be that far off.

Everyone says Live will be higher than USCF, but my USCF is higher than my ratings here, so I think its just kind of random.

On a somewhat unrelated note, in OTB chess when you put the opponent in check do you have to say check?

 Yes you have to say it out loud so everyone in the room can see you assert your dominance.

Yes.

In a recent G/30, d5 OTB game, with both of us in time panic mode, I declared mate aloud and my opponent obediently resigned.  The only problem was that it wasn't mate... but he had resigned, so too late.  (I had a winning position on the board, but given our time scramble, nothing was guaranteed.)  If he had noticed it was not mate, he probably could have gotten the TD to add 2 mins to his clock as a penalty on me for distracting him during his time trouble.

And, no, you don't have to say "check."  In fact it is considered poor form.  You also shouldn't go "Neighhhhhh" when you move your horsey.

I will have FIDE 1990, which is probably equivalent to around USCF 2040, on the next list. 

This means that I should hop again into my blitz pool. 2099 isn't good enough - I'm heading for 2640 now!!

Should be easy...

NO. There is no requirement to say check in OTB. People who say there is are mistaken. 

How can you compare OTB ratings at much slower time controls with blitz chess?  I have hardly ever played blitx chess -- on the internet or OTB.  Maybe 50 blitz games in 40 years, and maybe 20 games at 10/G 3d.  And I expect that mainstream blitz players would suffer if they switched to OTB chess at time controls of G/90, d10.  Some players do both, of course.  But the USCF also has blitz and quick chess ratings in addition to classical ratings, and in most instances the blitz/quick ratings are well below the classical rating.

Rapid, blitz, and bullet compare differently, and also the way the ratings relate are different for players under 2000 vs over 2000.

For Elo under 2000, chess.com rapid tends to be a few 100 points too high, while blitz and bullet tend to be within 100 points.

Another caveat is some players are particularly bad at one speed or another. So it's important to remember this is just in general.

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If you're interested in how you compare, my advice is not to worry about it. Ratings under 1000 just mean a beginner (or close to it). From 500 to 1000 isn't such a big difference, and you can close this gap by learning the basics and practicing for a few weeks. Comparatively 1000 to 1500 is much harder, often taking casual players years, and 1500 to 2000 even more difficult.

And then there's 2000 to 2500...