FWIW, there are some formal and informal processes. This is slanted toward GNOME, where I have most interaction.
The formal process I'm most familiar with is GNOME's "Friend of GNOME" stuff (http://www-old.gnome.org/friends/) and particularly their "Adopt a hacker" program.
Informally, hackers sometimes post their needs on planet gnome, e.g. when seif needed a new laptop and set up a paypal donation system so that those so inclined could pitch in. Some of the projects (e.g. zeitgeist) have a paypal donate button, and other hackers have things like amazon wishlists.