That's what worked for Vidalia and the GIMP. Last Friday, they asked people to build the app for the first time. At the anointed time, enthusiastic users hopped on to the project's IRC channel. By the end of the day, both projects retained new faces on IRC, and Vidalia's bug tracker had new patches attached. The event invitation felt urgent, by listing a specific time, and showed a willingness to bring new people on board; we think those were the keys to success. (Plus, you can read about the event in an attendee's own words.)"