Like all the hip kids I've been playing with Facebook and wondering what cool things will become possible now they've made the very smart move of opening up an API.
To help folks get started there are a couple of API Wrappers for Visual Studio developers which cut down a lot of the mechanics of working with Facebook and let you concentrate on building cool apps.
Thanks to Steve Clayton (MS) I discovered a really cool little app to sync my friends photos and birthdays to Outlook and thus to my Windows Mobile phone (though it works with anything that can sync to Outlook). What makes it even neater was that it was inspired by an "I wish" post from Jason Langridge (MS) and within days Ross had built it - using one of the MS API wrappers. There seems to be an MS theme going here!
I had thought the height of handy with Facebook had been their mobile interface but this is a great example of how the API is going to enable the reach of Facebook to grown and infiltrate everywhere the user goes. Now if only it could keep me up to date with phone number and email address changes it would be awesome (but Facebook respects my privacy and doesn't share that data at the moment).