I've been raiding with a friends guild on my Druid the past few weeks, but we've generally only done the first four bosses in ICC. The guild can't field a full 25-man raid on it's own so they've been relying on friends and a few pugs. Much was the case last night with a little more than half the raid being guild members and the rest being friends. We killed Festergut on the first night he was attempted. It took us eight attempts, but we got it done, but what really twirked a nerve with me was that we got him to 10% on the very first attempt. We had a few attempts where he was at 1% or less, and one attempt where he had 1800 life before we all died. We smelled blood and went for the kill on the next attempt after that 1800 health debacle. And boy did it feel good!
That just goes to show how important being able to execute is on these fights. My main guild has the same DPS we were running in last nights raid, so as I had believed, the difference came down to people not being able to handle the spores correctly. Pretty sad, but at least I've killed him on both characters now on 25-man.