I've just spent some time playing about with IE8 Beta 1 and have a few comments on it
1) The 'beta' tag is over-rated - it's nowhere near ready for a 'beta' tag.
2) It's very resource hungry - it was eating my CPU (AMD 64bit 2.2ghz) like crazy
3) (a follow on from point number 1) It crashes - a lot. 2 or 3 crashes per page load was the norm during my tests.
I know that it's beta software and supposed to be used by developers/designers to checkout the new rendering engine but it was completely un-usable for me. I've rolled back to IE7 now mainly so I can use the internet again