How many users one web server can handle?

U know  this is a good  question alot of servers out there when the internet started out had 2  1.7 GHZ processors as a server and could serve alot of "text based" webpages video however is more demanding but I would imagine you could still handle at least 50 or more users at any given time. I think your real bottle neck worries should be bandwidth..How big is your pipe? U know if you find your server being brought down by user demand and you are charging for memberships or whatever I imagine you could find venture capital and either buy a new server or rent one on say rackspace or Influxis.