I have sometimes laughed at myself for the meticulousness with which I log my rides. I am training, of course, but not for anything in particular (more self-irony).

But, when I injured my achilles tendon this spring it was really useful for me to have a log. I didn't really investigate the injury until about a month after it first happened (due to vacation and other stuff). But, since I had dutifully recorded my cramping calves and so forth, I was able to pin-point them as the cause. This further helped my doctor to determine that the underlying cause was with my feet. So, while making it an obsession is not a good thing, a few notes can pay off.

I am still trying to plot the relationship between my average speed and my sex-life, but I haven't found the appropriate Excel function.

Cheers,
Jamie