Damien Katz of CouchDB:

We don't want people who tend to ask "How can I contribute? What should I do?". We want people who identify for themselves what needs to be done and how they can contribute, and then do it. Our employees want to contribute to make things better, not for a paycheck, not for validation from a manager or even the community. They do it because they think it will make things better.

Damien Katz: Thoughts on an Open Source Company

He's talking about running a company based on an open source project, but the sentiment is valid for any project. There's a flip side too though; open source projects need to provide a structure where it's clear how people can contribute, make it clear that if you start on X or Y you're not going to tread on someone's toes.

It takes good communication on both sides, project and newcomer.