TDP rebates come out every once in a while, and each iteration has nuances designed to make redeeming the rebate as painful as possible. That said, if you're willing to jump through an excessive amount of hoops and install faulty software on your PC along with a valid credit card number (which I assume you had to do for the first rebate), then I've heard of some people getting multiple TDP rebates. But then again, when I looked at an SSD last December that included a TDP rebate, it specifically specified one rebate per customer. So like I said, just be sure you know what you're going into, as rebates in general can be a crapshoot and TDR rebates are particularly risky.

General rule of thumb: all rebates are gambles, never buy anything with a rebate that you wouldn't be willing to purchase at full cost. Because there's a chance that's exactly what you'll end up paying.