Eek! Looking through my old drafts I can't believe I forgot to post this. I was waiting for the LWN link to become available to all -- but I guess it's never too late to share the awesome.
Article: GUADEC: Banshee project reaches out for contributors (LWN)
This is the summary of a very good talk, "Inside the Banshee Awesome Factory" from last GUADEC, describing a number of things that the Banshee project does to attract, welcome and nurture new contributors. For instance, they make sure to make plugin development fun, by automating away the boilerplate code -- kinda similar to starting a new project in Django (I wonder if that's something Sugar could use, to create new Activities...) Every contribution is equally appreciated, including the "typo" fixes that many people would start with. They're not afraid to welcome people with little programming knowledge, and walk them through how easy it is to fix a bug or add a new feature. I suspect this works fantastically to also attract good people who are not overly confident in their skills. The speaker wasn't scared to live-demo how easy it is to add a new feature, particularly if it's similar to something existing -- actually he was a very good speaker, if you have the time you might want to catch the video of the talk itself (day 3, Paris room, 10:15-11:00).
A very cool stat I forgot about, that's in the article: in the last 2 years and a half of development, Banshee has averaged one new contributor every week. That is awesome! It's worth looking into what it is they're doing right.