Wowza, just backed my 100th Kickstarter project. Six failed to deliver but were relatively inexpensive. I'm also waiting on a couple that are now about a year late but still show progress. I think that's a pretty good track record and I really enjoy seeing behind the scenes on this stuff.
You very much have to go into it with certain expectations. Always research and get a feel for the creators, add ~2x the time for delivery estimates, and remember you're backing an idea, not buying a product.