Not really sure how I feel about them. Ever since Meshuggah exploded onto the scene with them on 'Nothing' I've not really heard anything to convince me they are the 'way forward' in riffing or guitar design. There is something about droning on the low notes that is extremely samey sounding. I don't know, maybe the current crop of bands using the instrument are just extremely derivative and uninventive, but the whole thing just sounds very homogenized to me. Guitars are pretty tough instruments to keep sounding clean. Even a 6-stringer can have this problem, so once you decide to keep adding strings, you just add to the clutter - to the sympathetic resonances. Having said that, the 6-string in concert pitch has existed for a long time. People have pretty much used it in just about every capacity it was ever going to get used in. Some deviation is necessary to keep things fresh for the new generation. I'm just unsure whether 'lower, lower, LOWER' is always better. I'm a middle-ground guy. My favourite tuning is Drop C#. Tight enough to thrash out, low enough to groove out, but not so far down that it loses the inherent edge it possesses by being a guitar - an intrinsically midrange-focused instrument.