Perfect timing for a flame war.... here's Laptop Magazine's article on Mac OS X Tiger vs. Windows Vista. Of course, in a week this will be almost out of date with the new OS/X release that's expected at WWDC. Of course as with everything, this is completely subjective... Vista's advances with it's pictures folder will mean nothing to say, pro photogs (who will use something like Lightroom or Aperture anyway), while to mom and dad wanting to organize snapshots, it might count for a lot. Gamers will probably still pass OS/X by due to the far greater availability of games on Windows (course, based on the benchmarks I've seen they'll pass by Vista for XP as well). However, it's an interesting view of 10 separate areas of each OS compared against each other.
One item I do disagree with is the networking discussion. My experience with Vista has been that copying and moving files around, even on the local system, but especially copying files to and from a fileserver (maybe this is MS trying to mess with Samba setups?) is d-o-g s-l-o-w. Unreasonably so. I'm pretty sure you don't need 10-20 seconds of "calculating time remaining" to copy a 100kb file from one folder to another. Also setting a folder to be shared seems to take forever as well... over a minute on a dual core 2.4 G machine.... f*king unacceptable IMHO. That said, I haven't had a mac for years and don't recall how their network setup is compared to the new "network and sharing center". I do remember things generally "just working" though.
Another item I disagree with is backups.... backing up a few files online with .mac is fine, but in this day and age of mass media, having a disk based backup is a huge advantage. That said, I haven't actually used Vista's backup, and would probably go with a 3rd party solution (trueimage or ghost or the like) anyway. Having online backup only isn't a winning position IMHO (assuming that OS/X only has .Mac as a solution of course).