I agree with Eyrei and Cyc on this issue. In my games, I always end up resenting the MPP, because it seems that more often than not, the AI signs them just before declaring war on someone you are trading with, and then you have to spend about five turns just trying to put your economy back together again.
The only time I look to sign an MPP with someone is when I need to get that someone into a war on my side and an alliance is not possible (ie. they are already in an MPP with my enemy...).
For example... I want to start a war with Babylon, but Babylon has an MPP with France, who I don't want to fight right now. I can't sign an allliance with France against Babylon, so I sign an MPP and declare war on Babylon. Then I just have to wait for the Babs to attack me and presto - instant ally.
and with respect to making the Iroquois our friend right now... signing an MPP with them will most certainly trigger a war with France and America. Not the best move at this point.