lets just make this clear, its certainly posted here already in many many threads...
if you read the unlocking stuff properly on the htc website, it clearly says that the warranty will be invalid for anything caused by unlocking the bootloader
so if you have a blatant hardware problem, ie the wifi antenna problem, they still have to repair it foc
so basically, unless you brick your device, you still have a warranty.
they might try insisting on replacing the main board for a cost, which i've heard quite often. the wifi fix requires changing the main board anyway, so for at least that problem, they shouldn't charge to fix.
still, it does depend on the type of problem as to whether you could convince them not to change the main board..