I've supported a couple. I think it's an exciting phenomenon. I only support ones that are started by someone whose work I've seen before. If a "name" supports one, I'm more likely to support it; that is, if a Monte Cook says he's putting money into supporting one, I'm inclined to take a look.
I think it would be worthwhile for those thinking of doing a Kickstarter, and who don't have a track record of some kind, to start off with a small project and make sure it gets completed in a timely fashion once funding comes through. I'm leery of supporting projects that seem really substantial if I have no clue about who is doing them. It's one thing to risk a few bucks on a small project, and quite another to support one with a $50+ buy-in, especially if it's by someone who is a complete unknown to me.
I'm still waiting for one project I supported to arrive. It's a few months late. I don't have doubts about it ever showing, but the longer it's taken, the more trepidation I feel about supporting other, similar projects.
I really dug that Steve Jackson did his OGRE Kickstarter and was so successful. I'd love to see other companies and well-known designers go and revive old properties like that. That is, I'd be inclined to support a game or product that put back in print something that may inspire a lot of nostalgia but be too niche-y for a company to think worthwhile.