I bought a laptop from Lenovo about a year ago (an IdeaPad Y550) and it came with VeriFace. From my experience the VeriFace software worked fairly well, if the room was well lit. In darker situations it failed miserably. I am not sure how they do the recognition, but it seems to be contrast and location of facial features.
Neat things: You can make movement a requirement for login (like you have to shift your head, open your mouth, etc) in order to bypass people using your picture to login. As for false positives, it seemingly had none. The nice bit is the system takes a picture of someone trying to use the VeriFace login system and stores it for your review at a later date. Not 100%, but surely good enough for standard consumer use.