Well, it's not really data mining but I wrote a program that would list the interests my friends have, ordered by the popularity of the given interest. As far as I can tell, LJ does not have robust tools for gathering said data, so I was forced to resort to HTML parsing. Yuck. The program has bugs, but it was a fun little exercise. I ran it for a friend of mine and curiously, he discovered that the most common interest for his friends was "cats", but he's not particularly fond of them. I, on the other hand, have a rather large number of friends interested in piercing, corsets, and candles (not the top interests, though.) I'll not speculate as to what that means.