It appears that HTC has been granted a patent on face to unlock on a mobile device with a front-facing camera.
Discussed here at:
Gotta Be Mobile
Here's the patent at the US Patent & Trademark Office.
The mobile device patent wars may be getting a little bit out of hand. There's more than one way to skin a cat. HTC should be able to protect its precise method, but patenting the whole face-unlock application world would seem to fall into the "obviousness" trap. Whatever you do don't click the obviousness link — it's a trap!