I bought Kami Retro, but nothing else so far on the Pandora. Also on other platforms I rarely buy anything - I bought "Cut the rope" and a few other cheap apps on my iPad, and a long time ago I bought (well actually my parents did, because I was still a kid) a few games for the Commodore 64. And that's about it.
In general, I don't tend to buy software. I prefer Free and Open Source software. Since that is what I like, that is also how I license the stuff I make myself. If people feel the need to thank me, a nice comment and/or a good rating on the repo is enough for me. If they really want to spend money, I encourage them to donate to the OpenPandora project (e.g. the preorder fund).