I too had never heard of application parts, or if I had they didn't turn on the the Idea lightbulb.
Funnily enough we have just been creating/cleaning up a library of common functions and basic menu forms between us at work.
It's hard work rationalising things when you have 4 similar, but different, versions of FileExists() type functions gathering dust in the corner of different apps.
Add a mint to the rogues gallery...