The only negative I've seen for a LFG tool would be ninja looting. Especially if a cross-server LFG tool as created. But there is a way to minimize ninja looting:
Add in - If you roll need while in a flashpoint, (or group for that matter), the item becomes bound to you AND the vendor value is reduced to 0 credits (must destroy item to bring up awareness that this item has no credit value).
This a little twist in a system in place in Rift. There all need rolls in groups cause the item to be bound. They left the vendor price in tact there, but just having it bound really helped reduce ninja looting. The one example I had was while in a group (just a quest), I noted that a recent group member was rolling need on the couple of items. We were low enough level where it really didn't matter (vendor value = 2 mobs worth of vendor trash), but he was off and on his way. Later he came back and said he got somethings for us in a dungeon. Giving the benefit of the doubt, we met him and when he tried to give them to us.... Bound. He didn't understand why and when I explained the system to him, he said "That sucks!" and we never saw him again. I did have him on my friends list and hoped he learned that "need before greed" works out best for everybody. But ahh well, not going to be upset that a ninja quit.
Adding the no-vendor value bit will keep the "at least I can sell it to a vendor" mentality down, and making people destroy an item (bit more obnoxious than just selling a 0-1 credit item) would discourage the behavior. The only ninjas left would be the flat out jerks out there that want to grief others... a much smaller percentage.
