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Rating on Chess.com
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2. doesn't really matter. I believe it's only used in selecting the tactis you're showed (if you rating is higher you will get more difficult puzzles).
1. I believe the more games you play, the less impact a win or loss will have.You should check the pinned post in the forum, it contains links to the glicko system and such. 
Lately I saw a worsening in my online play. I made a lot of tactics here and in other sites, but I don't really feel like they are useful in the game. Further also the rating of the Tactics Trainer is ridicolously high, some other friends are 2200, while being 1400 in USCF. And the same here they are 1800 or 1900 on blitz, while being 1300-1400 players OTB.
So it occurred to me the following:
1. The rating in chess.com is too high, they maybe should try to give only 7-10 points for a win/loss, instead of 100-150 like it happens in the beginning
2. Tactics Trainer rating also is too high compared to the reality of OTB play.
What is your experience?