You get one first-time deposit bonus for each site(assuming you either change your registry or find another PC to signup for the second Party skin). Periodically(every couple of months or so) they will have a redeposit bonus, or they may email you with a bonus code if you stop playing for awhile. I don't believe any of these bonuses work more than once.

There are several rooms that have monthly bonuses, not sure which I only play at Party and Stars. Check front page review or the Online Casinos topic for more info.