I am very annoyed at people who claim that there is absolutely no correlation between FIDE and chess.com and USCF and etc. How could there not be? Yes, OTB and online chess are different, and yes there are different pools of players, but people talk about them like there is absolutely nothing in common with them at all. Are people seriously suggesting that is as much in common with OTB chess and online chess as there is with soccer and poker? For all of those claiming that there is no similarity at all, let me ask you something- how often do you see a GM on live chess with an 800 rating?
The post that dug up a three month old thread. Worth it to say that? I think not...
Not to mention that my original post provided a fairly comprehensive answer to the rhetorical question posed - how there is no correspondence between a rating in one rating system and one in another.
Nevertheless the topic itself is evergreen. It seems there will forever be a steady influx of new acolytes for the cult of numerical symbology ... especially - and ironically - among the lower rating classes.
minor7b5 went on to "prove" that I'm wrong by repeating my point ... that the only meaning of ratings is the relative difference between them. Of course the best players rise to the top of any [valid] rating pool that they participate in. So will the least skilled players sink to the bottom, with those between falling somewhere in the middle. The specific numbers themselves, however, are meaningless except as a relative measure of past performance in competition with other rated players in the same pool.
Correspondence between ratings pools is strong - not exact - only when the rating system used by the pools is the same, the same initial numeric rating is used, the same - or very similar - K factors are used, there is a large overlap of players in the different pools, and the players have each played about the same number of games against opponents of the same average ratings in each pool.
My points are clear and irrefutable; the mathematics is solid. The many attempts to argue against them seem to indicate an alarmingly large population susceptable to the false claims of pseudo-scientific nonsense such as astrology and numerology.
Why all this emphasis on numbers? A 1400 player could easily be beaten by an 800 player if a game between the two reached a position that the 800 player knew very well how to play, but which was one of the many particular positions which clearly demonstrate why the 1400 player's rating is not 2000+.
Just worry about the quality of your play. If you're unable to judge that without using numbers, you have a lot of work to do, and you undoubtedly have no reason to brag about your own numbers or to mock those of others. If you are able to recognize high quality play, the numbers really won't mean all that much to you unless you're a bookie or a statistics researcher.
You should only worry about ratings when you're a titled player trying to make a living on tournament prizes, and only then because invitations to the best tournaments are based on ratings for some absurd reason.