I have been working on a small app lately (http://onlineqrlab.com). I'm giving it few hours a week and monitoring Google and back links traffic with Google Adsense.
I would like to know how people interact with my app, are they really happy using it, what other features they might be looking for....
I have found delicious to be useful, it provides data on who saved my app and thus was satisfied/happy using it (http://www.delicious.com/url/abbd7844f4b1fc741e29ab2707c69f4f)
Any other tools/techniques/methods?