I just tried an upgrade on my testing/dev blog page just to see if the svn/beta/rc version is getting there. I could see from the trac that it very close to finished now. :)
All went well, no errors of any kind during the upgrade.php etc, but when I tried to log on to admin I first get the opening page, then, if I go for my profile, write a post or anythin I get the error:
"You do not have sufficient permissions to access this page."
This might be a bug when upgrading but I am not sure as I only have tested on my dev blog. Not gonna do it on my live one just yet! :)