From the words of his friend:
— a lot depends on the type of site: commercial resource where so much advertising, donations almost not come, for a non-profit if done right you can earn a little bit. He estimates 1,000 visitors from 1 to 10 can make from 5 to 50 dollars.
it is very important how to organize. If you regularly remind visitors, for example, in the newsletter that the project needs support, the number of donations increased tenfold. And it is necessary to argue the need for donation, for example, large expenditures on infrastructure, and not just "very hungry".
just the Donate button is practically useless.
In any case, according to him on donate any large amount to raise is very difficult. Competent commercial policy on the same resource will give ten times more income.