I have a G11 and couldnt do without it. but then again I use ISBoxer and that has native support for it.
for example I have my shamans totems on the Gkeys in 1 block, I have oh shit buttons on another block so i dont have to press difficult button combos, I have buffs and stuff on another block. I just find it useful to have the extra 22 buttons ( and they can utilize modifiers too.. ) as hotkeys for ISBoxer.