I normally visit SO every day, but I rarely go to SF and SU, except to ask a question. In those two, I always get subscribed by e-mail, just in case i forget to get back and check for answers.
Now, in many cases, I get the answer in the same day and mark it as accepted. In those cases, I don't really need the e-mail to notify me the day after (and it's actually kind of confusing), so I propose to disable it for questions with accepted answers.
The reasoning here being "if I mark an answer as accepted, I've moved on, i'm no longer looking for another answer"
Just my 2 cents, may this is not that good an idea for everyone, not sure.