As discussed many times, the rebates are through Soyo which has a history of NEVER PAYING. Not like many rebates that you simply have to make a call, but these are the worst.
Their terms usually ensure you have to mail immediately but they wont begin to "process" until after the last purchase date, which can be as far as 9 months out. Of course they hope you forget about it.
Check bensbargains, fatwallet, resellerratings for more info on Soyo and their scams. (It's usually through TigerDirect, but also affects any place that sells their products). NewEgg also will not cover unpaid rebates.
Just be careful... buyer beware.