How does the operating system load balance between multiple processes accepting the same socket?

I'm reading the docs of the cluster module in Node.js:
http://nodejs.org/api/cluster.html

It claims the following:

When multiple processes are all accept()ing on the same underlying resource, the operating system load-balances across them very efficiently.

This sounds reasonable, but even after a couple of hours of googling, I haven't found any article or anything at all which would confirm it, or explain how this load balancing logic works in the operating system.

Also, what operating systems are doing this kind of effective load balancing?