Logins are easy to track. They happen only once per user session. So it's easy and efficient to find out how many users are logged in at a given time.  e.g. login, increment the counter; logout, decrement the counter (conceptually--might not actually implement it that way).

But keeping track of what board, i.e. what page, each user is on in real time would require continuous monitoring & logging of every user session. Right now there's over 30,000 of those. Then collect statistics for each board and reporting them, again in real time or near real time. I'm sure it can be done, but it wouldn't be trivial and I'm not sure we'd like the impact on response time. Maybe we could all chip in a buck to buy a big hunkin' server, and some programmer time to do this.