Back in May HTC announced that all their future devices would be able to have their bootloaders unlocked via a software tool. The company provided a general timeframe for the tool's release last month, pointing out that it would be a gradual rollout, and today the HTC Sensation has become the first to get OEM-sanctioned root access.
For now the tool is limited the European version of the phone; Owners of T-Mobile's HTC Sensation 4G variant in the U.S., as well as the EVO 3D, will have to wait a bit further while testing is conducted on their devices.
You'll need to register for an account at HTCDev.com and accept legal disclaimers telling you that unlocking may void all or parts of your warranty. It doesn't sound too encouraging from the get-go, but then again, those interested in rooting their devices to install a custom ROM are likely aware of the risks. The unlocking process will also require that you have the Android SDK to get a device token to plug into the web app, after which you will be emailed the unlocking key.
HTC's in-depth instructions can be found here. Let us know your thoughts if you follow the process or, conversely, if you've already unlocked your HTC device with the help of unofficial tools such as unrevoked and AlphaRev's Revolutionary: S-OFF & Recovery Tool.