I'm no longer getting e-mail notifications either. They were working.
I'm sure this is not the cause, but notice that this forum is powered by SMF 1.1.11. Well, version 2.0.7 is the latest, although the SMF website says that 1.1.19 is still considered a current stable version.
I guess the admins have taken a "if it's not broke why upgrade" approach as well as "if it's broke, why care" approach.