I'm a bit confused as to why we don't have one.
It's similar to how phpBB or IP.board forums implement it.
Basically, at the bottom of the page, you can see the registered users that are currently logged in on the website.
Visitors that are not logged in count as guests. Except bots which are a different category alltogether.
You could also color the username in their respective rank (black for platinum, yellow for gold, etc).

This way, you could solve the forever headaching question of "when to upload?", as now you can see exactly how many users are online.