You'd be surprised, Hborre.  I tried the built-in ISF and found that the resulting brightness was so blown-out that I'm tempted to suspect faulty math on the part of the developers.  I say that last part only because I seem to recall testing it out on some very simple textures, too, so I'm quite sure it's not my shader that's causing the blow-out.  I'll try it again, though.  If you and BB are using it without problems, there's still a possibility I'm doing something wrong and just don't know it.  Stay tuned!