Blog statistics. Some people admit to looking at them, others won’t (even though we know they do :-)) For some they can become the all-consuming passion – especially if you’re trying to monetarize your blog.
Lorelle on WordPress has a very useful page that collects together the various different plugins and schemes for WordPress that collect statistic. See Counting WordPress: Statistics WordPress Plugins « Lorelle on WordPress.
I’ve been wondering for a while how many words I’ve written each year, and now I can find out.