It seems to be an unfortunate reality of WoW, if not MMORPGs in general: When a new patch goes live, more often than not, it's going to be a bit rocky on the servers for a while. Patch 2.4.2 is no exception, Many servers are having trouble staying up, including most of the Ruin Battlegroup, which according to a few our tipsters has been having more than its share of trouble lately. Blue Poster Vrakthis has assured posters on the Customer Service Forum that the Realm issues are being looked into, but so far, there does not seem to be a solid reason for the downtime other than, hey, it's patch day!
EDIT: It has now been confirmed that the downtimes were intentional for the purpose of emergency maintenance. The downtime should be minimal.
As of the time of this writing, the following servers are down: