I tried it, but the problems I found were that parts of IE Pro wouldn't work properly with it.
Certain sites took ages to load (You could get round this by using compatibility mode) but I found it a bit of a hassle and to be honest the new features such has web slice doesn't appear to work on Ebay like the demonstration showed it to on Microsoft's site.
Overall I found it a big fuss about something that is very similar to IE7. I might update to IE8 when the new features on IE8 are working on more web sites and also when other add ons are fully compatibly. My advice is to wait until the little bugs etc are ironed out. I got the impression that IE8 was still in Beta?
Overall I find IE7 a lot better that IE8. Its easy enough to go back to IE7 if you find you don't like IE8. You simply uninstall IE8, you then have back IE7, that's exactly what I did.