I went to a Billy Joel & Elton John concert over the summer armed with just my Sony a200 and a 75-300 f/4-5.6 lens. I have a 50 1.7 but I was traveling light and I knew that would not bring me close enough to my subjects even though I had very good seats. I wouldn't suggest using a fast prime with little reach like a 30 or 50 unless you have front row seats, unless you are more concerned with getting the ambiance than actually seeing the performers' faces. Even though I used a very slow (and cheap) telephoto, I came away with plenty of very usable (though not superb) shots. Here are a few tips:
-Shoot at a variety of shutter speed and ISO combinations (I think it goes without saying that you should shoot wide open! So keep it on Manual or Av mode). Although most of your shots at 400 or 800 will be blurry, you'll probably have one or two that come out sharp, and these ones will have less grain too.
-Overexpose by 1/3 stop or 1/2 stop - it reduces the noise a bit.
-Shoot RAW! It's hard to get a properly exposed shot a lot of the time when the subject is so bright and the background is so dark, so I did a lot of Camera Raw tweaking on my photos.
-Right now I use Sony which has sensor-based image stabilization. I wouldn't suggest shooting without some form of IS, especially if your lens is slow like mine.
-Shoot in burst mode! I took waaaay more pictures than I needed.
I hope these help! Here is my album of the concert on Flickr, and you can look at the EXIF data on the pictures to get an idea of what settings I used. Some of them are cropped.
http://www.flickr.com/photos/sammers05/sets/72157621591197237/