Windows7 and Ubuntu 9.10
Unlike in the previous experience with Windows, the Windows 7 performs really well. Regarding Ubuntu, it's better than 9.04 (I was happy with 9.04 as well). The only funny thing is that I had to find drivers and manually install my ATI Raedon X1300 VGA for Windows7. Earlier I used to do this for Ubuntu installations :)
For the moment, these two OSs seems to be a great combination if you are planning to get the best of both worlds.