Currently i’m working on a OpenSource GIS project called Majas. a javascript(dojo) application for editting your geographical data online.
I’m building a module to make majas communicate with openstreetmap.org
I have only little project experience, but what I learned here is: SPECIFICATION/DOCUMENTATION FILES ARE IMPORTANT.
I did learn some other stuff too. However I mainly had to use Basic Java stuff, it wasn’t that easy to get to know the whole majas core code
Curious about majas? look here