I'm not sure how you got confused before, but neither of the two prior "prebates" has been taxable in any way. The two prior ones were prepayments of retroactive reductions in current year's taxes, as is this one. It must be accounted for when you file your return to make sure you don't get the benefit twice, but in no way is it taxable, nor does it have to be "paid back."

I was a college student at the time, so I was going based on something I read on the internet, which is never a good idea I guess ;)