On the new Win7 machine I built last year, I have two RAID-0ed Intel SSDs as my OS drive (along with important programs (games)), and you can pry them from my cold dead fingers!
The machine is very fast to boot up, nearly instantly drops to the desktop, and I can immediately click all of the programs in the taskbar and they all quickly open up.
SSD drives are probably the best general performance upgrade you can make for your PC... They make everything snappy!
