The Mac App Store gave me an excuse to try to make money out of my Open Source gravity simulator, Gravit.
I signed up to the Mac Developer Program, packaged Gravit, and uploaded it. Soon after, I got an email mentioning:
2.5 Apps that use non-public APIs will be rejected
The following non-public APIs are included in your application:
CPSSetFrontProcess, CPSGetCurrentProcess and CPSEnableForegroundOperation from the ApplicationServices.framework