Need Some Spring Apps Ideas for VMforce!

So a few months ago I promised to put together a Spring / Chatter / App Engine demo that could be possibly ported to VMforce. Since our Handbook is off to the printers, I'm back to doing fun stuff!

I'm looking for some ideas for a demo project that you typically wouldn't do natively on the platform that you would like to eventually see on VMforce. Perhaps a customer facing Java app with a jQuery front end for HR, eCommerce or whatever.

Please send me your ideas!