A minor typo in a php file managed to squeeze its way into the release (CRM/ACL/BAO/ACL.php, line 799 or so there is an extra 'x')
So we've released CiviCRM v2.0.1. We took the opportunity to fix a few other minor issues. We expect to do bug fix releases every other week for the next few months.
Apologies for the messup. Folks who've downloaded 2.0.0 need not feel compelled to download 2.0.1. Please use the following patch for your distribution: ACL Patch