Personally I'm not sure i'd put credits in a web app. I dont know really why. Strangely enuff, I do like the idea of an easter egg approach. Perhaps its the hacker in me.

I do however like the idea that was posted about having a "Cool code board". In places where I've worked, I've encouraged the sharing of design/code philosophy, snippets and what-not, and have found it not only helps others in the team, but the recognition and appreciation of peers goes along way to keep/maintain/improve confidence and ability in the team.