The OS shuffle...I have a PC Audio Labs 8-core, circa early Vista. They recommended a removable drive bay for the system disk so I could check out 64-bit Vista, but revert to XP if (in their words) I needed "to get real work done." The Vista drive pretty much became my Sonar/Sony Vegas drive, as they were early 64-bit programs.

I added a Windows 7 OS disk several months ago, so I now have access to all three operating systems. The Vista one hasn't been used since I switched. I used XP a lot at first, but now I use it 5% of the time, if that. There's lots of stuff installed on XP that I thought I would miss, but only ReWire really mattered, and that will be taken care of in a couple weeks. If I really miss something while doing a project, I'll re-install it on the Win 7 disk. Slowly but surely, all the good bits are ending up on the W7 OS drive.

Once ReWire happens, I really can't think of any reasons to go back to XP. 64-bit W7 with Sonar has far better performance by just about any measure.