Engadget ran a great how-to on how exactly you can download tv shows automatically. It's a bit tricky, since the software uses regular expressions, but they provide a bunch of examples to make that easier.
I've often heard this can replace a PVR completely, but if anyone's ever looked around for missed shows online, you can probably agree the quality usually isn't too high and you'll likely have trouble finding what you need unless it's somewhat popular. Still, it's an interesting direction and a few years from now the home recording fans of TV may just fill out the remainder of the TV lineup (and in HDTV no less). I know the networks and movie studios are freaking out over this, so it'll be interesting to see what they do in response to kill this technology.