According to chatter in /2 WoW has been having issues the last few days. People have been complaining of lag across WoW and Diablo, there's been glitches with RealID, the reporting system was totally busted at one point and things like that. First thing is disable your addons and make sure it's not addon related. If it's not addons {and seriously, test it, don't just say it's not addons because they didn't cause problems before or because no one else is reporting addon issues. Not that you would, but you'd be surprised how often I see that} then go look at the WoW forums for other people reporting disconnects.

With all the complaints I've been hearing, there's bound to be a few posts up that mirror your disconnect issue.