Sometimes after you get booted from the pit, you can go get some wide angle shots from the audience side. But don't piss anyone off, if you get asked to stop, then do so, and move to a new spot. Watch your metering closely, it's very typical for the talent to be lit up by spot lights, and if you use your auto metering mode, even if you set your focus point on the subject, it'll adjust for everything else being really dark, and you can easily blow out the talent -- metering in these conditions takes practice, and there's a load of different ways you can go.
If the lighting is consistent and not too spotty, I'll use the auto matrix metering somtimes, or partial metering, but if it's really hairy, I'll use spot metering, but that's not available on a lot of cams. The other thing you can do is meter off of the same thing consistently (using exposure LOCK), then recompose and take the shots. With that method, you can review your histogram to see if you are blowing out the highlights, and then use exposure compensation to lower your exposure by some amount -- then repeat by metering off the same thing as last time, lock the exposure (the "*" button on canons), recompose, take the shot, and then review your histogram. The HISTOGRAM is your friend in tricky lighting, learn how to read/use it if you don't know how already.
Also, watch out for your white balance. Don't use auto WB in the crazy lighting of concert shows. Pick a preset, most likely tungsten, or set a custom WB. Not only will your color be probably more accurate than auto WB would produce, all of your photos will have a consistent WB throughout your shoot cause you used the same preset -- as opposed to letting auto WB change the color with every shot potentially. Also, shoot in RAW if you can and if you have the space on your mem card cause that'll let you completely change WB after the fact, not to mention other benefits (although this opens a can of worms RAW vs. JPG that many people would argue about, so just my opinion there).
Another thing (if you don't know this, otherwise forgive me), is if it's real dark, you'll want a fast lens like f/2.8 or lower, and you'll probably want to shoot in aperture-priorty mode with the aperture locked fully open (at the lowest f-stop to let in the most light). Then, set your ISO as low as you can while still getting hand-holding speeds of AT LEAST 1/60 second. Personally, I'd shoot for more like 1/100 or faster, which might require you to be shooting at 1600 ISO if you can.
Last tip... While in the pit, make sure to turn around and shoot the audience a little -- those can be great shots, and a lot of times you can do that before the show starts while you're already up in the pit, so it won't take away from your three songs.
Good luck!