A few games on the console allow you to record your sessions and upload them for others to view. You can do that using a few tools on the PC, but Valve's building one into Team Fortress 2
Today, the Replay Update
will let you cut up games that are recorded on Record-enabled servers and share them on Steam or Youtube. You'll be able to edit the videos from various view points combining them into a movie that might even win you a Saxxy.
What's a Saxxy? Why Valve's holding a two week contest
that ends by midnight May 20th GMT where you can win a little Saxxy trophy in one of twenty categories. So get to some playing and brush up on your editing skills. I really hope this gets added to other Valve games, especially Left 4 Dead 1/2