Well I thought it'd be interesting to have a look at Facebook for developing an application - give that it's already got a huge userbase.
I won't go into details about the project that I'm wanting to set up eventually - as today was just about having a little gander at the API and working out what could be done.
The facebook stuff is rather complex - and I'm not really a programmer - so most of that went over my head. I did find a good site which explained how to create a facebook application in 5 minutes. Well, whilst not strictly a facebook application (as all it does is run inside facebook rather than using the API) I had it set up quite fast, and can be viewed (and added) at http://apps.facebook.com/chaostheory/.
It doesn't do much, and I doubt it'll ever do more - but it was a nice test for the purposes.
Now it's on to actually looking at the API and starting to do something that actually uses it :)