If you revel in data (and who doesn’t! , check out Technology Review’s article on How to Use Twitter for Personal Data Mining. Even if (like me) you’re not a twitterer (or do you call that a twit?), this is a nice introduction to data mining using nothing more complex than text editing and a simple visualization tool.
The techniques described here are applicable to lots of other data sets too (including perhaps the promised history of your Facebook wall posts: my account doesn’t have this feature yet, so i don’t know what this will look like).
Even if it seems silly to analyze what you yourself have said, it’s worth thinking about the data tracks we all leave around now, and what we (and others!) might do with them.