I've contributed, but only to projects that involved fairly well-known established print-published writers/artists who had some experience with solo/shared production of e-works whose stuff I either really wanted because I'd bought "regular" works from them previously and/or had a good reputation and the pledge with decent rewards cost was low enough that I was willing to throw a small amount of money at them.
For a relative-to-total unknown, I doubt I'd even be willing to look, much less take the chance. I did pass on several vaguely-interesting but I-don't-know-this-person-and-what-kind-of-quality-they-really-produce projects (and I missed the deadline for a couple of others I was somewhat-interested-but-dithering on and mostly don't really regret).
Personally, I don't think it would be a good idea to rely on crowdsourcing your funding unless you really have an already established and loyally supportive audience and a decent set of quality works under your belt.
For the record, I supported: 1 mostly-already-written-but-not-otherwise-economically-viable-to-finish fantasy novel by a favourite author, 1 multi-author shared world anthology, 1 multi-author shared world anthology with accompanying role-playing-game, 1 reprinted how-to artbook with new extras by the original author, 1 educational graphic novel anthology by established comic book artists, one of whom is a favourite.
Missed and regretted: 1 AU historical steampunk novel follow-up to a print-published series by an author I've never read but was willing to check out and will probably keep an eye on her next related project; 1 feminist science fiction anthology being assembled from the works of classic established writers like Joanna Russ et al. by the editor for a small press whose official e-book edition I'll probably buy on sale when it comes out.
Missed and not regretted: 1 tie-in by Big-6 established author to some print series of hers (I was interested, but the price was too high for a pledge that got me the free e-book versions of the novellas she was going to write); 1 novel continuation by small press established author of some fantasy series which again set too high a price for bare minimum e-book reward and I didn't have time to check out the writing to see if was good enough to merit the $15-25 being asked.