Completely agree.

@Droob : Yes and no, for sure, if you look at the BSD license or the MIT or whatever, there is not reciprocity implied, but if you look at the GPL, there is. If you look at that piece (http://www.gnu.org/licenses/why-not-lgpl.en.html) for example, it's pretty obvious there is a certain "brotherhood" mind implied.

But I think that even if there were no reciprocity implied, giving is more or less morally mandatory (for the bandwidth, hosting cost, etc) ...

I agree with you. However, just because something isn't implied, doesn't mean it's not a good idea to do it. Charity isn't implied, but it's obvious we should do it in order to help people in need.

We all do open source because we simply love it and want to give a gift, like you said. However, whenever people give me a gift, no matter how bad or good it is, I feel it's my duty to at least say "Thanks!"

It can be a lot more selfish than that though. I contribute to projects because I want to get a better product as a result - even if it's just to test something or document an issue, or providing answers to the community.