Raids are a tricky thing. You have to have good tanking, healing, and DPS in the right proportions, people who listen and prepare and pay attention. You have to get those people online and motivated at the same time, and you have to be able to learn from your mistakes and change your strategy for the better. Most important of all, I think, you need a great raid leader.
When I first joined a raiding guild in BC, I was thrilled with the raid leader. He was Australian, so it was great listening to his accent over Ventrilo. I remember him as being very cool-headed and completely on top of what was going on each pull. If we wiped, he'd tell us what had gone wrong and what we were going to do to fix it, and he led us to many victories. He played a tank, a tiny gnome warrior with a shield nearly as big as he was, but he had alts of almost every class and he knew all their abilities perfectly. When he eventually decided to leave WoW due to real-life issues just at the start of Ulduar, the guild tried to go on without him, but it just wasn't the same. I eventually left and went through a few guilds with mediocre raid leaders before finally founding my own. Now I'm once again lucky enough to have a great raid leader, a paladin tank who studies the fights, analyzes the data, keeps his cool and quarterbacks our raids to victory.
What are the qualities that you look for in a great raid leader? Do you need someone calm and relaxed, or does a fiery raid leader push your performance to the next level? Is raid role (tank, healer, DPS) a factor in a leader's quality?