Here is the post by Taproot ED on the real cost of Facebook Causes ($300 million in nonprofit employee time to raise $30 million): http://www.taprootfoundation.org/blog/2008/07/is-causescom-r...
I think the interesting point is that most nonprofits judge ROI over the life of the donor and use sophisticated CRMs tied in with their other online fundraising efforts to judge their efficacy.
Causes did a typical Silicon Valley move by disintermediating the nonprofits as nodes in the Causes network which robs the nonprofits of valuable data about their constituents.