Man Garrosh is so frustrating, and it's intentionally designed to be that way. You have to go through 7-8 minutes of easy shit before reaching the hard part that is much more hectic and takes practice. So you get maybe 1 or 2 minutes of practice at most for each ~15 minute attempt.
The issue my current guild has is the latter part of phase 2 with the empowered whirling corruptions. Some add or two always ends up empowered and either kills someone, or takes too long to kill, resulting in a lot of lost boss DPS. There also seem to be some healing issues around the second or third empowered whirling corruption if we make it that far. Only pushed it to P3 once tonight, but with something like 7 people dead already. If we can get there consistently, zerging him down with the second lust should happen sooner or later. MCs don't seem to be much of an issue unless there's adds still up.
But we probably had at least 4 or 5 pulls (about half) comprised early on by this dumbass ret pally who kept dying to the iron star in P1. He was removed from the raid and then gquit (that's right gquit, not booted) right after which was kind of hilarious but not undeserved. I mean some people you just can't help and if they weed themselves out, I suppose that's fine.