I've had the exact same experience with Extrabux as Ricky. They still owe me as much as $258.60 (I am not kidding!) for purchases they acknowledged (!) I made through their site. They refuse to post cashback, and, after my repeated inquiries, they stopped answering my emails altogether. And email is the only way to get in touch with them – they don’t publish their phone numbers anywhere. Stay away from this company; make your purchases through a site that may not promise you the moon, but one that actually pays what it promises. MrRebates, BigCrumbs, Ebates and FatWallet are all reliable. Extrabux (and its sister site BargainMatch.com) are not! Stay away from them!
P.S. @Noah_A: If you cared about your customers like you claim to, you would at least respond to their emails and make sincere effort to investigate their inquiries and report the results back to them. In my case, you had three months (!) to rectify the situation, but you chose not to. As for your claim that "this is a common policy among all cash back sites" - well, I've made numerous purchases over the years through each of the sites you mentioned, and was paid *every time*! So evidently, if one wants to run an honest cashback site, it can be done.