Better power management under Linux than Windows XP
Speaking of Windows XP, although in some instances it is a good OS for coding, it always makes me a little uncomfortable having so much stuff installed by default. Although I wrote a commercial Windows product (SAIC ANSim) using Windows 1.0 beta and delivered on Windows 1.0 and 1.03, Windows NT was the first version of Windows that I liked. I had a "secret" for using Windows NT effectively: I had one boot partition that was totally stripped of everything but my software development tools and another that I would load a bunch of junk on - the trimmed down version with no spurious applications installed was incredibly stable. I have thought of doing the same thing for Windows XP but I don't think that XP's copy protection would let me do this.
I used to use a shared FAT32 partition to share design artifacts and source code between dual booted operating systems, but now it is just so much easier to keep everything in a CVS repository on a server. As I mentioned the other day, this makes it easy to use Windows Linux, or OS X for a task, picking the best platform per job.