Compared to Windows Vista I find that Ubuntu's user interface is much more elegant and doesn't come in your way of doing useful work. If I had to rate the OSes for desktop today, I would rate them as:
I have been playing with my Mac-mini for a couple of years now, and it's growing on me. Shraddha will ditch her Windows XP machine and start using the Mac-mini as her primary desktop machine from next week. So there are only two Windows machines still left in my house. One is Windows XP which is my primary desktop and it will remain so for a long time, until I find a good alternatives to Adobe Photoshop Elements and Adobe Premiere Elements. I'm thinking of buying an iMac as my next desktop. The only reason I am not yet putting Ubuntu on my primary desktop is the lack of software available for Video Editing. Adobe Photoshop Elements is available for Mac, but Premiere Elements is not. I am also thinking of buying Final Cut Express for Video Editing along with the iMac I'm thinking of buying. May be in another 12-18 months I'll replace my Windows XP machine with a new iMac. The other Windows machine has Vista, which I've setup for Isha. The only reason her machine is Windows desktop is because the online games she playes are only supported on Windows platform (bad Disney).
If Isha can live without the online Disney games that require Windows Media Player, then I can be completely Windows free in a couple of years! :-)