For fun, I downloaded the Windows 7 Beta DVD ISO from Microsoft. I made a second partition on my second HDD, and installed it. It was painless, and didn't take long.
Windows 7 is, so far, running like a champ. It seems about as responsive as Vista, no worse in my unscientific opinion. It recognized all of my hardware, such as my TV tuner card, video card, and monitor, and is talking to my network. It is the "Ultimate" version, which means it comes with Windows Media Center, which is nice.
If you have about 16 gigabytes to spare, give it a whirl it isn't bad.