What's the difference between Silver, Gold and Platinum memberships?

Silver membership is a basic membership providing you with limited number of ads and limited payout and withdrawal facility. 

Gold membership most important features are unlimited ads (subject to daily availability) and access to HTML code. You can also submit as many payouts as you want once you reach the payout cap. 

Platinum membership provides all in Gold membership plus an increase in CPC (how much you earn per click) to $0.02 and no limit payout request and no payout cap.