The LK, both normal and heroic, slew three of my guilds in WoTLK. The first guild couldn't kill him on normal, which lead to not being able to even down the first wing. The second guild got to him early on, around the 5% buff, but had a pattern of wiping in p1, then wiping 2% before the RP event. The third guild took awhile to get to him, but even with the 30% buff, couldn't even get past the first transition. All of them decided they'd sooner just disband then go 10 man. My guild in TBC was destroyed by, inc surprise, M'uru. Another of my guilds died in Ulduar to who would get Valanyr first. An officer swapped to healer because we needed them, and was angry he wasn't picked to get the first one over a healer we had since we started raiding.