It's important to keep in mind that volunteers - anyone you're not compensating for the work - do what they want, and won't do that they don't want to. A lot of volunteer organizations implode when people at the core forget that.
An excellent example of someone reaching their tolerance level on stuff they don't want to do for free (althought it's commercial-ish work on an unfunded project, rather than a purely volunteer project for charity):
http://www.27bslash6.com/p2p.html