I am working on a little project using Arduino: a "Facebook notifier". It's a simple device, that looks like the typical american mailbox: when you receive a new notify, a little flag connected to the box raises. In this way, you can check if there are news on Facebook without connecting manually to the social network.
On my blog
the specific post), you can find all the details, the diagram of the circuit (very simple) and the source code of the necessary software.
It's just a simple project, but I hope it's the starting point to build more complex devices.