I'm still plowing through the ballet performance photos, with the help of Lightroom. I have the demo version, but I've decided to purchase it, as it's proved to make workflow with hundreds of photos SO much easier than using Photoshop.
The performance was in the, hmm, atrium? of a fancy retirement home. The backdrop is an indoor area with plants, lamp posts and a fountain. Very cluttered.... not ideal for dance photos. Also, low light - unideal for taking photos of moving subjects.

One of the dancers lent me his Canon 5D, the next step up from my own model. I previously relied on automatic focus, but he recommended a different technique; telling the camera in advance where I wanted the focus to be, so it didn't have to spend time searching for subjects to focus on (which is slower and less accurate). So... I had to predict where the dancing action was going to take place, focus there, and then take the photo when the dancer moved into that spot. That, plus ISO 1600 (grainier, but better at capturing motion), on aperture priority f/2.8 or so (good for low light situations), seemed to do the trick! Oh, and there's the improved camera body too.