Metric for concurrent users/server?

When looking at server numbers from Facebook, Youtube or Linkedin, it would be nice to have a metric to compare concurrent users/server over several architectures (becnhmarking). Is there something like that?

Stephan Schmidt Administrator
CTO Coach , svese
Stephan is a CTO coach. He has been a coder since the early 80s, has founded several startups and worked in small and large companies as CTO. After he sold his latest startup he took up CTO coaching. He can be found on LinkedIn or follow him in Twitter.
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