I pulled a fresh copy of WordPress yesterday from SVN (7693), and noticed that the installation process cannot be completed because users aren’t being added to the database correctly. To be more specific wp_userdata gets filled out correctly, but wp_usermeta is missing a few entries. Only “first_name” gets INSERTed into wp_usermeta, the rest of the entries are UPDATEed according to my mysql log (which of course fails since wordpress is trying to update entries that do not exist). Unfortunatly “capabilities” is also an “update” which means that no user can log into the admin panel (including the automatically generated “admin” user in the installation process).
Workarounds till this is fixed correctly: add the missing rows by hand directly into the database.