A word of warning:

Don't do it :-)

I'm v.guilty for using all the latest technologies so a few weeks back I installed IE9 Beta.

Problems encountered:

MVC2 projects getting 404 a lot, I did see this discussed in an interview with Phil Hack and there was a debate on wheather IE9 was just too fast for MVC2.... do you buy it??

Also I've been having problems with the editor I use to write my blog posts, been using raw html as it just didnt work, tonight i tried and compatibility mode and it works again :-)

What have I gained... nothing new that i'm using.... until I get some time to run through HTML5  (on a months holiday from work, wedding next week and putting final touches on the new house... time constraints ey! )