Methinks someone needs to investigate some more heavy guitar sounds. :p

As for a 7-string, I wouldn't want one personally. I have enough trouble handling six and don't need to add to my confusion. ;) But there are tons of things you can potentially do with a seven string that you can't by detuning -- like, uh, get a low B and keep all six of your other strings. Detuning works fine for D or drop D, but when you get down to B, things can go a little wobbly.

If you're good enough to use it, the seventh string just gives you another weapon in the arsenal. It's not for me, but the guitars that I use or you use are probably not for other people on this board, either. Play what you feel comfortable with and let everyone else do the same ... works better that way.