The yahoo group Stashbusters http://www.stashbuster.com/ has optional challenges you can participate in. I have never participated in the no buy, but my buying habits have been altered by all the thoughtful discussions I have read in the group forum.
I participated in the UFO challenge a few years. Basically there is a running list of participants when your name comes to the top of the list you are UFO Queen. If you don’t complete a UFO during the week of your reign you have to send in a penalty fat quarter. Every time you finish a UFO your name moves to the bottom of the list. You must finish at least one UFO every quarter. If you don’t finish a UFO in a quarter you send in a penalty fat quarter. To start the challenge you submit 2 fat quarters. Every quarter some names are drawn from those who completed UFOs and those folks receive some of the fat quarters as prizes.
I have made a quick tally of my UFOs. I have 23, though there probably are a few that will appear when I dig deeper. 9 of those are donation quilts, and 3 of that group just need binding. I had already planned to finish up a bunch and turn them in to guild in January, so I am in a good position no matter where my name appears in the list (random to start) Jan 1, 2011.
Saturday a friend came over and learned how to use the longarm. We quilted one of her UFOs and now she just needs to complete the binding.