The above screenshot shows how I currently use Hermes. The bartender bars are set up in the same arrangement as my G13 and I monitor the cooldowns on my main (pally in this shot) using those. I too am not a fan of cooldown bars and have moved away from them in my UIs, preferring to use buttons.

Above the bartender bars is Hermes, tracking 6 cooldowns (although having Chain Lightning there is pretty pointless) on my 4 shaman slaves.

I see an immediate use for the drag and drop functionality in mirroring the key layout of my G13, but for my slaves. Of course this wouldn't work as simply for a mixed-class group.

Another use for the drag-and-drop might be to allow custom ordering of the spells being monitored.

I have some ideas for dragging-out spells. Will post again after I have played around with some mockups.