Windows.Next/8 to have Facial/Movement Recognition.

If the leaked presentation images are real (and if they aren't, thats totally what MS should do anyway), then you will be able to sign in your computer by just......being in front of it, switch users in the same way, turn PC on/off faster than ever before, and more neat stuff:

Microsoft is getting ready to release Kinect into the wild this holiday season.
Next windows is expected to come ~2011, so they will probably have many features built into windows using Kinect technology.
Can't wait to hear more of it D:

Source:
http://msftkitchen.com/2010/06/windows-8-plans-leaked-numerous-details-revealed.html