The other weekend I was doing photography for a couple in the church, and what with one shooting photos inside and outside in rapid succession, I eventually ended up with a bunch of photos that were horribly overexposed.
Fortunately, I use Adobe Lightroom, which works really well with my Canon EOS30D's RAW file format. RAW files store the data directly off the camera's sensor, unlike JPEG, which throws away large chunks of it to keep file sizes down. Lightroom can access all that data, and rescue many an otherwise-ruined picture; here's what 60 seconds in Lightroom will do for you.
Of course, it's not perfect - the bridesmaids' dresses were actually a pale green, but the picture was too overexposed to rescue that. The solution there would be to paint the colour back in using Photoshop, but since I can't afford the scandalous markup that products sold in Australia attract...
The moral of this story (other than checking settings before a shot and then checking the result afterwards) - if you use a DSLR, use RAW always.