Since it looks like there are many DVR/PVR software solutions out there now, I am going to try to put them all in one post, making it easier to see what's on the market, and how it compares. So if you know of any stable solution which turns your PC into a DVR/PVR, please post them here.
Free
Windows
Meedio TV ( http://www.meedio.com )
MediaPortal ( http://www.team-mediaportal.com )
GB PVR ( http://www.gbpvr.com )
Got All Media ( http://www.gallm.com/default.aspx )
Linux
MythTV ( http://www.mythtv.com )
Freevo ( http://freevo.sourceforge.net/ )
Mac OS
Mac Media Center ( http://mrzippy.org.uk/macmediacenter )
Commercial
Windows
CTpvr ( http://ctpvr.com )
Xlobby ( http://www.xlobby.com )
Microsoft Windows Media Center Edition
Beyond TV ( http://www.snapstream.com )
SageTV ( http://www.sage.tv )
ShowShifter ( http://www.showshifter.com )
SesamTV Media Center ( http://www.sesamtv.com )
TVedia ( http://www.8dim.com )
Linux
SageTV ( http://www.sage.tv )
Mac OS
Free
Windows
Meedio TV ( http://www.meedio.com )
MediaPortal ( http://www.team-mediaportal.com )
GB PVR ( http://www.gbpvr.com )
Got All Media ( http://www.gallm.com/default.aspx )
Linux
MythTV ( http://www.mythtv.com )
Freevo ( http://freevo.sourceforge.net/ )
Mac OS
Mac Media Center ( http://mrzippy.org.uk/macmediacenter )
Commercial
Windows
CTpvr ( http://ctpvr.com )
Xlobby ( http://www.xlobby.com )
Microsoft Windows Media Center Edition
Beyond TV ( http://www.snapstream.com )
SageTV ( http://www.sage.tv )
ShowShifter ( http://www.showshifter.com )
SesamTV Media Center ( http://www.sesamtv.com )
TVedia ( http://www.8dim.com )
Linux
SageTV ( http://www.sage.tv )
Mac OS