I was wondering what kind of payment models people have tried and what has helped make them effective. Recently I started to give away a free game on my site to help increase traffic. Not being a total fool I added a donation button to the official page. A lot of people have asked for features and I'm thinking that it might be a good idea to put up a donation thermometer and mark it "feature x when I get $25, feature y when I get $50," etc... Have any of you tried something similar? How well did it work? Feel free to discuss any other payment systems, too.