Bump map can be used to add lighting to badly lit shots.   I'm using it right now to add lighting to some church footage that had terrible lighting.  It does a really good job.
The first thing you need to do is turn off the bump height when you add it.  Change it to spot and start playing with the beginning and end of the light (in the little white box).  Also play with the Intensity, Ambience and Focus.  I've found that with some footage (especially HDV) you may get banding if you have a dark background (in my case dark blue curtains).  In that case I jumped over to After Effects which has better lighting effects.  All in all this a great little effect which can work wonders on some shots.
Marc