There will be extended maintenance today, April 1st, on all the realms from 3:00 a.m. PDT until 11:00 a.m. PDT. Hopefully this will fix many of the issues appearing over the past week – and just give the servers some breathing room. There have been many bugs reported, some of which you can read about in the various hotfixes that have been pushed onto the servers in the past week.
Also, this downtime is not an April Fool's joke. It has been expected.
Of course, we don't know what the Blizzard April Fool's joke will be yet. When we do find out, we'll get word up right away here at WoW Insider.