It's interesting how the New York Times is portraying the charity social networks like Jumo and Causes as the new United Way. This concept of the new gatekeepers occurs across all industries. For filmmakers and authors, Amazon will offer to manufacture and sell your product for you and give you some percentage of the proceeds. Apple has a similar deal with iTunes and iBooks.
The problem with all these types of services is that you don't know who your customer/donor is. You don't get their email address, the gatekeeper does. So the next time you have a fundraising drive or release a book, you can't go back to those people again -- the people most likely to buy your book. That is, unless you pay the gatekeeper. Amazon actually has a paid service where you can promote your book to all the people who have bought some other book.
You need to be able to process your own donations on your own website. You need to be able to sell your books, DVDs, CDs, and whatever else all on your own site. That's the only way you can truly be independent and build for the long-term.
I dealt with this problem at Brave New Films by building out a whole distribution infrastructure with fulfillment, shipping, an online store, and connected it all with our supporter database and website. But who wants to do all that? This is one of the core problems NationBuilder is looking to solve for independent leaders and creators.