There is nothing more lame than getting stuck in a group that just isn't going to work. If you're a warrior, and you get put in a group that has a feral druid, two rogues, and a warlock, odds are that you're in for a rough night. I'm not saying it won't work-- maybe the druid has crazy healing gear, and the rogues are a few levels high for the instance, and the warlock is really good at doing all the things they can do. But if the group's not there, it's not going to happen.
But sometimes, you can get a really amazing group from what doesn't seem like the right makeup. I once ran a group with three shaman (me as a resto, and two elemental), a mage and a druid, and lo and behold, we actually finished Stratholme easily (we were all 60, before the expansion). And I've always wanted to run a group of all shaman-- two resto, two elemental, and an enhancement, through one of the 5 mans. I'm sure that if we had the gear and the know-how, we could make it work.
So what's the wackiest group you've ever been in, where you thought you were just plain doomed-- and yet, it worked? I'm no good at the math, but with
eight nine classes (told you I was bad at math) in five spots, that's a whole lot of different groups out there. What is the craziest one you've had that works?