I see some potential in this AddOn, even if it is very simple (I was actually considering writing a similar one). What I would like to see is an option to reduce your DKP when you receive loot, here is how it would work:

-Did someone just receive an item? If yes ->
-Was it you who received it? If yes ->
-Are you in a raid group? If yes ->
-Is the item quality above [set minimum item quality]? If yes ->
-Popup window asking how much you got it for, and then reduce your DKP with that amount.

Another option would be to simply add or remove DKP without having to manually figure it out (laziness ftw), say using /adddkp XX or /removedkp XX.

I'm afraid I'm not using this AddOn yet, but I love to give other people ideas :P Good luck!