AppEngine is fun. I've been fiddling on a number of personal projects using it lately, some involving BoardGameGeek. A month ago, I posted there, but forgot to post here: I made a fun BGG collection comparison tool. The combination of the BGG XML API and AppEngine with urlfetch (and ElementTree) makes writing BGG "add-ons" pretty easy. I'll certainly keep writing more, but other people should write some too. Don't know python? Well, it's a nice language and worth learning. :)
And, to get you started, here's the (sloppy, not cleaned up, but functional) bggcoll.py library for fetching collection info from BGG. It lets you do things like:
coll = bggcoll.GetCollection(username)
while doing all the nice things like stuffing it in memcache, the datastore, and only refetching it from BGG if the local copy is stale.