Single User Login enabled for administrators
This week, Single User Login was enabled for all administrators, allowing users, after migration through the system, to log onto any public Wikimedia wiki with the same username and password.
Unification occurs via Special:MergeAccount, a new special page. There, users will be asked to provide their password; this password and their e-mail address will be compared to those on other wikis; those that match will automatically be transferred. For those that do not match, users can submit more passwords (in the event that the additional account(s) are valid, but have different passwords).
In the case of impostor accounts, users are currently unable to automatically usurp those accounts, for security reasons. Users can request that bureaucrats (or stewards, for small wikis) usurp them manually, allowing the administrator to reclaim them. However, after unifying an account, impostors cannot be registered under the same name.
The feature is only available to users who are administrators on at least one Wikimedia wiki, and to access the feature, must visit Special:MergeAccount on any wiki that they are an administrator on. It will be enabled for all users at a later date, but in order to work out any bugs in the system, and roll the system out slowly, developers decided to limit the number of users who have initial access to it.
Single User Login is also not available for any private or "fish-bowl" wikis, including WikimediaFoundation.org, and internal, board, staff, ArbCom, and other wikis where account creation is not open to the public.
There are many outstanding bugs with the new system; first and foremost, local control on user accounts is broken in some ways with global accounts. According to developer Tim Starling, "The new user log, IP blocks on account creation, and AntiSpoof conflict checking are broken." Also, users must log in manually to each wiki; Starling hopes to allow users to log in once for all wikis, and fix user account controls, in the future.
Other bugs may not be fixed right away; preferences and e-mail addresses do not change from one account to the rest, and global accounts currently cannot be renamed. Starling "won't make any guarantees" to fix those bugs, although other developers may work on these.