From the "OMGWTFBBQ" department comes a tale of mixed up raid ID's. Seems that two members of the Alliance guild Conquest on Kilrogg ended up in a BT raid with Horde guild Temporary Insanity. The forum thread contains many interesting screenshots for you to puzzle over. If these are digitally edited, they're done well. Bluetracker allows you to skip to the part where Tigole steps into the thread and informs folks that Blizzard is looking into it... what I personally want to know is, was this just a random glitch or 'insert conspiracy music here' is Blizzard trying to test some kind of cross faction raiding on us? Are we guinea pigs for their diabolical schemes?
No, probably it was just a bug, as cool as I think cross faction raids could be. I especially like the suggestion in this screenshot of cross faction raiding with everyone flagged for PvP. Imagine a raid where you could accidentally, or even purposefully, frag your fellow raiders? Or a raid where horde and alliance players actually had to race to the end boss, perhaps even sniping at each other along the way? Being that I'm starting to PvP more and more lately, I'd find that an interesting change to the raiding/PvP mechanic. Imagine that, instead of racing to opposite sites of Alterac Valley, you both had to race to the same place to kill the same guy.
At any rate, the folks of Conquest and Temporary Insanity got to do what almost no one else in the entire game has, namely they've confronted Illidan, the end boss of the current game, with a cross faction raid. That's one interesting bug.