Probably about 6.
I am rarely gone for that long, nobody really PMs me, few quote me, fewer do the mention thing, I don't get notifications for likes (not that I get all that many of those if I am not writing on the portal) as I am not a fan of likes systems and were I in charge it would be gone as my first proper move, I don't get such things when people doodle on the profile bit (never read that either actually -- usually I will only see it when I accidentally click on it doing something else), and I am subscribed to all of 2 threads and a staff forum section, one thread not even being that active these days. Never liked the friend/follow system either so none of that.
Other than the staff section (which is 3 a day on a busy day) most things I get are for when my old 360 release posts or something get landed on and I get a notification for that. Those mainly being because I have not figured out how to turn it off yet.