A crash bug was discovered involving the Demon Hunter and her Templar. Thanks to Gamespot UK for the tip. Quote from Blizzard’s known issues page:
While playing a Demon Hunter, if a shield is equipped to the Templar follower, you may be disconnected from Battle.net. You may be unable to login, receiving the message “Error 3006”. We are currently investigating this issue, and further updates can be found on the 1.0.1 Known Issues thread.
A hotfix is already being propagated to the realms, which all appear to be down for this patch.
Now that was a worthy adversary!
If you want more info about bugs, crashes, and other technical delights, check Bashiok’s twitter; it’s pretty much non-stop with those all day today.
Update: Technical issues and the downtime continues on TA region Tuesday evening. Bashiok recommends using global play to start a new char on Asia or EU realm while waiting.
Update #2: @Diablo reports the realm was back up and trouble free by 11:21, well ahead of the 11:45 estimate. (Words we never once heard about Battle.net realms during the Diablo 3 Beta test.)