have you tried checking Profile -> Notifications and Email? maybe something changed in there.
This is the first thing I did. The only thing that MAY have changed there is "Automatically watch topics after replying to them" is unchecked, however, my watchlist is still intact and I'm not getting notifications for items in the watchlist, either, so that change wouldn't be directly related to this issue if it is indeed a change. I also confirmed that my e-mail address hasn't changed (would be really bad news if it had, but I did check both of these things before starting this thread).