I've been dual-boxing with a G-13 for a month or so now and love it! It's very easy to keep track of what keys do what and it's pretty comfortable to boot.

Having three separate keysets in one profile is great too. I keep one set for dual-druids, one for dual hunters and the third for mixed pairs.

I would NOT want to go back to playing WoW (even running a solo toon) without it.