Manual isn't as much of a nightmare as you'd think really. In some gigs I find it's best to use manual due to awkward lighting, then you know you can tinker in post if need be. That being said, a lot of the time I have to use AV because the lighting changes so much. It's actually VERY frustrating at times when I have a plan in my head to take a specific style of photo that suits a B&W processing style I want to apply and due to lighting changing it all goes pear shaped
Generally I'd say it's as mrk says and it's all experience. When I go to gigs around the area, I get to know the locations and start with what I used in the past. I often see photographers from local papers covering a band and having the problems I had when I first went to the location. I don't think you ever stop learning though as there are so many things that cause problems with exposure at night gigs. Sometimes I just wish it was out in a field at night so the light doesn't bounce around
Personally I'm not the quickest at changing settings on the fly, so I only use manual where I've got a lot of control or wiggle room in post.
Also I've decided IS should be illegal except on macro lenses. It's peeing me off on my 70-200