I've backed 6 projects, including 2 that are still active. And I plan to back a lot more.
Why do I back projects? I am an artist, writer, and small press publisher, so when I see high-quality projects in those areas, I try to support them as best I can, Good rewards at a range of pledge levels and good presentation are two of the biggest factors for me, but social value is also huge. For example, a project like Maxx Giffens' The Transformation Project (
http://kck.st/1V8d4lQ he's documenting trans individuals at different transformative stages) is well put-together and, if funded, will have a positive effect on the world. Sproutlings (
http://kck.st/1M24cdf)--a book of stories and poems about weeds that includes Alice in Wonderland and "carnivorous flora" among its inspirations--just sounds awesome.
I also back projects because people have backed mine for The Quilliad. It's only fair. As someone nearing the end of a campaign and knowing that feeling of relief when the goal is in sight, I want other people to feel that too. I like knowing my money is going toward increasing the creativity available to us in the world.