[jwr]

I would pay if I found the library better than the free alternatives. Specifically, I would pay if the library allowed me to reach my goals faster: simple, well-designed, not doing too many things and well documented and maintained are the key factors.

One reason for paying is to ensure that the library is maintained: too many people out there assume that labor is free.

I would not pay for anything that isn't open source, though, because I do not want to become fully dependent on something that might disappear.