Not to stir the poo pot again ... but shrug. Flashing your phone does not void the warranty. Just like installing Ubuntu on your Win7 Dell Laptop doesn't void the warranty. If you're THAT worried about your warranty and your phone has to go back to Sprint, reflash it to stock.
Now, that isn't to say that Sprint has to warranty the non-stock software you've installed, either. Their response to "omg i flashed my phone now it sucks" could be "well we can restore it to how it came from us if you want" or "oh well that sucks for you". Either way, if your screen backlight dies or the internals(CPU RAM etc) die, chances are you'll be covered without a fight - and if they DID put up a fight, they'd lose any court case, because they'd have to prove that the new software killed the hardware. See: Magnusson-Moss Warranty Act.
I agree w/OMG_WTF_BBQ though - I'm going over to the EVO, not because of "OMG APPS"
but because I want a phone I don't have to beat into submission to make it work.