When MS came out with Windows 95 it was a big quantum leap in the right direction. GUI was poor in the windows 3.1 days. Something that Windows has going for it is plug and play. It works nicely for the average Joe using Office and doing a little internet browsing.
I am a Windows user experimenting with Linux and having a good time. Linux is certainly not for the average Joe yet. There is still too much text file configuration and programming-like things to make things work well.
With that said, the difference between XP and Vista is not like the difference between 3.1 and 95. As I sit and look at upgrades necessary for Vista I am thinking...Why? My XP box does everything I want it to do, now MS wants me to upgrade to a new operating system for getter graphics and animations, all window dressing IMHO.
Linux will conmtinue to keep it's committed core because that core likes linux for what it does - solid tailor made configuration of the OS the way YOU need it, not the way the average Joe needs it. Don't get me wrong, I am having tons of fun setting up this linux box to be my backup server and proxy server/internet access filter. It has breathed new life in this old 800Mhz box that was running crappy Windows ME slowly. Slackware is so much faster!
Bottom line...Migration will be much slower to Vista because of the cost/benefit balance. It is just not what it was in 1995. Unlike 1995 when the migration happened because it was a better product, Microsoft will force the migration by phasing out XP, not because it represents a big, worthwhile step in the right direction. Also, mark my words, there will be lots of security holes that pop up!