For the stats-junkies out there, here are a few interesting visual representations of who is federating, and how they're doing it.
(Hover over graph segments for quantities)

Deployed Versions

Proportion of registered organisations running each version of UC product

16 403 165 775

Cloud vs On-Premises

Proportion of on-premises deployments against hosted/cloud solutions

114 950 308

Federation Security

Split of registered organisations offering open vs. closed federation

1440 405

World Domination!

Just look at that global coverage!