Rake kickback

[young nut]

This might be kind of a newbie question, but I've only been playing on the online poker sites for a few months. But I've heard people talking about getting a portion of their rake back from the site. Is this true for all the sites? And if so, how much of a kickback do you get?

I play on Pokerstars and Partypoker, but I haven't heard anything from them about rake kickbacks.

[SevenStuda]

Sign-up bonuses are often considered rake ruductions/kickbacks.

-Dimitri