It's not really comparable as its been around for longer (I think) and has always been pretty large. But the Ultimate Guitar forums I used to frequent - anything posted in any of those forums would drop to page 2 or 3 within an hour. In the 'pit' (or 'not related' forum) you could expect to see 100-200 new topics an hour at peak times.
Though, it has to be said, they've all died down since social media took off like has already been said...
Most people join a forum to get help with a specific problem. Those of us that join to help others or get a kick out of helping someone else spec up a system are starting to die out
edit: in fact, I just logged onto my long dormant UG profile to see if the narrative holds... in 2009 every topic on page 1 would've been from within the last few minutes. Now, within the first 10 results its '9 hours ago'...