Future quote from Blizzard:
During the character migration last Thursday, several characters have become temporarily misplaced. At first the character migration occurred flawlessly, but under heavy load at peak times, the character migration experienced performance issues which have resulted in stability problems on certain realms, minor rollbacks and a problem with character retrieval upon login that some of you have reported.
Naturally we do not consider this an acceptable state of play for our customers. We are working around the clock to diagnose and remedy these problems. As a temporary solution, we encourage you to create a character on the unaffected realms. This is a short-term solution and, while undesirable, is in place to keep the realms more stable while we work on the main cause of the issues.
During the regular maintenance window that is scheduled for tomorrow, we will be making some additional changes that should allow us to further screw everything up on the affected realms. Our team is committed to resolving these issues as quickly and efficiently as they can, assuming it doesn't cut into our 15-minute breaks. In the meantime, we appreciate your patience and understanding.