I have a book I published using Leanpub and I set the minimum to be $10. Some people pay the minimum. Some people pay the suggested price of $15. Some have even been as generous as to pay MORE than the suggested price.

If I ever decide to give away my book for free for a limited time, I would not feel bad about people giving me $0 when they could give me whatever they want.

I am in agreement with Raganwald in that I just want people to read it and find it helpful.