Okay, another strange one. In this case, there doesn’t seem to be a KB regarding it so it is 80% gut feel and 20% confirmation from Spence of similar behaviour. The problem is, after applying (seemingly/timing wise and based on 2 environments to date) Service Pack 1 (SP1) to SharePoint 2010, if you create a site collection, you may get an access denied error and are unable to login as a site admin until you assign someone different and then reassign your account. The key to the problem appears to be that if you have a root site collection configured with the publishing features (say, your corporate Intranet) and then you have managed paths with site collections under them that serve as typical team/collaborative sites, you may run into the above system, particularly if you haven’t fully configured the necessary/desired cache (superuser/superreader) accounts.
Well, okay, to be fair, SP1 simply aggravates an existing misconfiguration (in other words, it probably should have been defined properly before 😉
Mirjam van Olst documents the fix here – http://sharepointchick.com/archive/2010/10/06/resolving-the-super-user-account-utilized-by-the-cache-is.aspx