Typedia: A Shared Encyclopedia of Typefaces
This is a brilliant piece of motivational design on Typedia, a wiki-esque encyclopedia of typefaces. Right on the top of the site, they greet you with 3 things you can do to make Typedia a better site. These are generally related to building out the completeness of a typeface's page (providing examples, or gussying up the page's presentation.)
There is obviously some primary value here (if visitors actually do these things, then the site benefits!) But there's a sneakily-awesome secondary benefit as well: just by virtue of seeing these suggestions, it's already imprinted upon your mind that this is a community effort site. This is a site where you're being asked to contribute in a positive way. The corollary may also be: jerks need not apply.
Even if you don't ever take up one of these Good Deeds, their presence helps set the tone for your engagement with the site. If you want to be a helpful person, this may be the place for you.
(The language helps too. It's friendly and approachable.)