Wow, call this download Friday. If you are not distracted enough playing the Orange Box or Bioshock, you may as well get busy during the weekend with new demos of Call of Duty 4 (list of mirrors) and TimeShift. I believe the former needs no introduction, not for nothing it's going for its fourth iteration. The demo includes one level from the single player campaign.
TimeShift is also a first person shooter, developed by Saber Interactive, this game places you in a more modern setting which is touted as 4D as you can slow, stop and reverse the flow of time, a.k.a. space-time continuum.
Certainly not a bad way to spend time while we eagerly await for Crysis' release (or Guitar Hero 3 for console gamers for that matter).