Who says user-generated content is only for the web? According to their website, JPG magazine is aimed at "people who love imagemaking without attitude." The magazine is built around a website where you can submit your best photos. Community voting determines which photos will make it into the print magazine which has six issues per year.
As far as I know, JPG is the first magazine that's built from user-generated content. Are you aware of anything else like this? It's an interesting concept and worth keeping an eye on.