I had the exact same experience. I worked for an open source company that had bounties and I think it was one of the major factors that completely killed the open source community around it. A few years later a friend of mine mentioned she had contributed to the project, but stopped after she worked on something for 10 hours and realized that worked out to about $10/hour.
However, it seems like a good model if it gets up to market rates (if someone could do this in an hour or two) and especially if it's something developers wouldn't do on their own.
However, I think it's a great idea in principle. There's been the "street performer protocol" http://en.wikipedia.org/wiki/Threshold_pledge_system#Street_... (which didn't seem to take off); and http://www.kickstarter.com (which did, but it's mostly not software).