(It sounds unbelievably anal-retentive, but I've always been a list maker: of normal things like books read & movies watched, and of stranger things like 'coincidences'.)
Harish, knowing of such heavy logging, pointed me to this Wired article about how many people seem to be doing this, and are using the Web to record & share such information. I began noting this info so as to better understand what influences my health and to spot & prepare for seasonal & other factors. I have a large mass of data now, but perhaps not a lot of insights.
Still, I continue to do so largely because I think I like recording information. Leading a trivia-monger's life smooths away any objections to pointlessness - why, someday, all of this may come in handy.
I'd really like to get my hands on some of the tools mentioned in the article - when, with each step I take, a bean counter wriggles in ecstacy.