Check your notification settings for your watched forums and topics
I noticed I wasn't getting notifications of replies to topic that I had posted in. I also wasn't getting notifications for new posts in forums I'm watching. Have had others message me about this, too. Turns out this is a "known" issue with the upgrade; known to developers but not to me!
But no biggie-- the fix is easy: just check/reset your notification settings in your control panel.
Watch my short screencast that shows you how to do this ==> http://screencast.com/t/v2oCSzRdY