http://play.golang.org/p/yjqyCAEMyR

What is the expected output?

I expect all examples to listen on an IPv4 address. On the playground this is the case.

What do you see instead?

net.Listen("tcp", "0.0.0.0:11111") listens on [::]:11111 on my
system.

The full output is:
2014/02/25 19:59:14 0.0.0.0:11111
2014/02/25 19:59:14 [::]:11112
2014/02/25 19:59:14 127.0.0.1:11113
2014/02/25 19:59:14 127.0.0.1:11114

Which operating system are you using?

Ubuntu 12.04, 3.8.0-36-generic

Which version are you using?  (run 'go version' or 'gccgo --version')

go version go1.2 linux/amd64

The only reason the examples use different ports is because the playground doesn't
Close() quickly enough for the program to succeed (it works when I Close() locally).
From testing, I don't think port number makes a difference to the behaviour.

Admittedly the workaround is trivial, but I thought this worth reporting anyway.