I see lots of "Donate" buttons on websites which are not donations to charity as such, but of the form "Donate to this website in order to help keep the website running" or "If you like this website, please donate some money". For example, Tineye has
Has TinEye been useful to you? If so, please donate!
I confess that I have never donated to any. I also don't feel like my website is a worthy enough cause to display a begging bowl. Does anybody actually make money off their "Donate" buttons? Specifically I mean those sites where it says "Please donate some money to the author if you like this website" rather than "Please donate to a worthy cause" (e.g. Red Cross, Unicef etc.)
Hard data please!