Ladies and gentlemen, minutes ago HTC announced that they have been listening to us all along and will reverse their stance on locking bootloaders! The statement comes directly from the CEO Peter Chou and reads:
There has been overwhelmingly customer feedback that people want access to open bootloaders on HTC phones. I want you to know that we've listened.
Today, I'm confirming we will no longer be locking the bootloaders on our devices. Thanks for your passion, support and patience," Peter Chou, CEO of HTC
Devices with locked bootloaders can still be rooted and usually partially unlocked. They could even enjoy custom ROMs (see the Droid X ROM community), but because the system kernel cannot be replaced, these ROMs cannot be considered complete - they can change things on the surface but not under the hood.