I thought I'd drop by to share some opinion. The subject said it all really. I just managed to get the Windows 7 RC installed (admittedly with a lot of hassle), but from then on it was smooth.
The thing I like most? Windows Media Center was the easiest tuner setup I've ever experienced. It's fast, has decent features (such as optionally recording a series as opposed to a single show) and isn't remotely laggy. Compared to the experience I had with PowerCinema, it blows it out of the water.
The only thing not quite clear was that using a USB tuner I had to select "Cable" without a set-top box as the input option. Only took about ten seconds to work out however.
Try it! It's great!