Here an interesting article by Benjamin Mako Hill

Abstract

It's easier for a successful volunteer Free Software project to get
money than it is to decide how to spend it. While paying developers is
easy, it can carry unintended negative consequences. This essay explores
problems and benefits of paying developers in volunteer free and open
source projects and surveys strategies that projects have used to
successfully finance development while maintaining their volunteer nature.

<http://mako.cc/writing/funding_volunteers/funding_volunteers.html>