Thinking about buying a HDTV tuner card for my PC, and was curious about how this interacts with the 360 when the 360 is used as an extender. Am I able to play around with the tuner controls (such as timeshifting, setting timer records etc) in realtime through the 360? Or is the only thing I can use the 360 for is playback of already recorded TV files? Just looking for some clarification before I commit.
Any feedback?

With regards to TV, the 360 can do everything that you can do on the PC with Media Center. The only differences you'll have is with codec support for videos.

The 360's media extender functionality basically looks like you are running Windows Media Center. You can do almost anything that you can do with WMC on the computer. And yes, that includes the guide and setting up recordings, etc...

Last I heard, just about the only thing you can't do remotely via 360 that you can do directly at the PC is play DVDs. Not sure if Vista now allows it or if there's a tweak somewhere to enable that...