Well if I had one, I'd prolly use 1-5 for attacks most commonly used and mouse buttons for CDs, but I guess it depends on what you're used to and what feels most comfortable to you. anyway GZ on the mouse.
Right now I just use my naga for pretty much everything except for chatting and of course modifier keys, sense the side buttons are by default bound to 1-= like my action bars, I didn't even have to rearrange anything.
My missus and I both have one, they are awesome - has even managed to break my missus nasty clicking habit!
1-6 on the Naga for my main attacks, s1-s6 for CD's/CC's/pots/stones, 7-12/s7-s12 for situational things. a1-a6 for things I do rarely.
I keep my racial activation on the exact same button on every char - no longer use my keyboard for any actions, only movement, targeting & modifiers.
We have both gotten so used to it that I'm thinking of buying a spare in case any of ours goes tits up in the middle of a raid, I don't think we could plug a 'normal' mouse in.