I do buy the paid versions of apps, when appropriate. According to
AppBrain Android Market - find the best Android Apps and Games , I have spent almost $30 on apps:
god_kratos's Apps on the phone. However, there are a couple that I have bought outside of the market that are not included in that such as TiBU Pro (or donate or whatever he calls it...), LauncherPro Plus, and I think one other one, but cannot remember what it was.
Most apps have free versions and they are good. Some of them have features included in the paid version that warrant the purchase. Others (TiBU and LauncherPro specifically) are such great apps that I don't really even care about the paid features, but instead want to support the Dev's so that they are motivated to continue development of the apps.
If no one ever bought the paid apps, then the market would die. No dev's would ever want to code apps if they are never going to be compensated for their hard work.
Now, I did buy the paid version of Advanced Task Killer Pro for the auto kill feature. However, after about 3 months of use, I decided to disable it and see what happens. I don't use it any more. Now, that doesn't mean that I am upset about my purchase. This is because the Dev is really good at what he/she does and I am happy to support dev's who work hard to make quality apps.
Anyways, that's just my 2 cents.
Kratos