Yes, they've done studies. The results were reported in an issue of Scientific American Mind a few months ago, but I can't remember where the original study was done...if I get some time later I'll look it up.

If I rememebr right, it works by somehow training the person to control brain activity. When the seizure tries to move back and forth between hemispheres, the training kicks in and stops it or slows it down. I don't think it eliminates anything, but it does reduce the severity.