Unlocking is not illegal - or at least I can't see how it could be. You don't sign any agreement in the store when you buy it. You just pick it up and carry it to the register, pay for it and leave. You don't choose a plan, you don't make a commitment to do anything - you just buy and leave. As mentioned above, the DMCA has a specific exemption clause allowing unlocking of cell phones for the purpose of using the device with a different service. Since it's legally valid to bypass the lock, and I didn't agree to anything in the store, I don't see the issue.
There's a patch to enable YouTube again after the unlock - it's a simple, one-click affair - not hard at all.
As far as firmware updates disabling the lock again - this is highly likely. But there's a checkbox in iTunes that says "don't check for updates". Besides - there's not much I want fixed on the phone. Better Flash support might be nice, but beyond that... I'd be happy enough not to ever patch it for firmware.