An idea just hit me, whad'ya think.
So you join a random dungeon as a Tank, and you specifically joined to get DPS gear (your tank set is maxed out from raiding). When your group gets to the first boss and kills him, a DPS item drops that you need, a DPS specifically needed that item also, but with the new system of Need or Greed it's no problem.
If you're the tank the need button will look something like this
[Armor of Awesome Dps] : Need (offspec) Greed
If you're the DPS it won't have the (Offspec) in parenthesis, so even though you and the DPS both rolled need on it, and the other 3 people rolled greed, the DPS will win the item because it's for his main spec for the dungeon.
The nice thing about this is it won't create extra buttons to choose from on loot which I think blizzard specifically want's to avoid, and it will also fix ninja problems and make everyone happy. The DPS will see you also wanted it, and a conversation can carry out between you 2 to see if he can spare the piece for you if he's nice enough, without causing problems.
This will help so you don't have to get in the way of someone who needs it for their main spec, but will win it for your personal use over people who just want to sell it.
---------- Post added 2011-06-14 at 03:02 PM ----------
-If I was still playing WoW i'd post it on the official forums, but I don't so if anyone thinks it's a good enough of an idea, go ahead and copy paste / reword it w/e and put it on their for me.