I used the free version for a couple months and then upgraded to Pro - $30 is nomimal for the great features you get. It works well (on my site) and has nice stats. Much better than Bannerize, the other one I tried. The support is fantastic too. Nice to get a reply within less than an hour instead of posting on a forum and hoping/waiting for a useful reply.
Frankly I probably never would have donated to the free plugin out of pure laziness, but I am more than happy to pay for PRO whatever the reason. I wonder how many people that are taking the time to complain about the free version, took the time to donate.