I have observed a striking correlation between blogging, interest in emergency medicine, and geocaching. First in myself, then Doc Shazam, and now Jaime Marks from the Differential went on a GPS hunt with her EM attending and a nurse.
OK, my n is 3. Still, it seems like these are naturally overlapping interests, and I can't offer an explanation why. It's worth noting, however, that none of these activities were possible until very recently.