Just a thought on something I've noticed in commenting at some of your blogs and elsewhere:
When I begin typing various letters in those CAPTCHA boxes*, Firefox helpfully suggests to me some of the past strings I've typed, and I can't help but wonder how much such completely useless information my computer has saved up in various nooks and crannies.
But then, how much do I have myself? And more importantly, which of us has more?
Regardless, I suppose saving the entries in CAPTCHA fields isn't always useless. Recently it helped me remember that one time I was asked to type out xgvzd before commenting somewhere, and that other time I had to type xftwp... what heady, groundbreaking times those were!
* I got rid of mine a couple weeks ago, to stop annoying everyone, and I haven't yet had to deal with any spam comments at all.