How do chess site ratings compare?

Many times in this site we have discussed how do USCF ratings compare to online ratings. On the other hand, lately I have noticed that online site ratings when compared to a players strength might actually vary form one site to the next. I'm sure this is directly proportional to the audience who uses the site, but for example:

A 1500 player in sites such as yahoo, FICS, and WCL might be comparable most of the time. But a 1500 player in ICC or chess.com seems to play at a much higher level. I'm not sure how this would compare against the USCF rating....but having played against 1500 rated players in tournaments I think:

USCF 1500 > yahoo, FICS, WCL 1500  ....but then... ICC, Chess.com 1500 > USCF 1500

I know this doesn't include a major statistical analysis, but I'm interested in hearing about your experiences.

Of course, the answer is that these are always "apples and oranges" comparisons, but ... you might check out my hardly-scientific mini-study.

My USCF and Chess.com rating(Standard) are close, I seriously wonder how someone can have 1500 here and about 1000 in USCF. I would think FIDE rating 1500 is stronger than USCF rating 1500, but who cares, isn't just a number until you are master level or even close to master level? and Psychology may play a role in the difference between OTB and online ratings, anyone else agree? 

"...I seriously wonder how someone can have 1500 here and about 1000 in USCF. " -duskrevival

It's more common than you think and the reasons can vary. For example:

- People get nervous while in a tournament environment

- Online they play at time controls in which they are more comfortable at

- While playing at home, every now and then they might seek help. For example: A friend or family member sitting next to them, or a book for openings (more on this later), use the aid of software.

- I know a couple folks who use the Internet as a way to improve their opening repertoire, and they actually use books while playing the first 8-10 moves. This usually minimizes their chances for opening blunders online...but in a tournament is another story.

- As for chess software...I'm sure some folks use it. Have you ever had a game where you have an advantage over your opponent (material or positional) and all of a sudden your opponents takes a long "thinking break". Then, when he starts playing after the break...it seems you are playing against a vicious grandmaster who was not at the board before. Hello Mr Fritz!!

Personally, for about 2 years, my USCF rating was around 1200 while my online ratings fluctuated between 1500-1600. The major gap for me was that I wasn't used to attending tournaments...and the writing and hitting the clock was a little nerve racking. It took me a while to get use to write down the moves and hit the clock after each move. Once I got relax about those 2 things, my USCF rating eventually increased and paired up with my online ratings.