Here in NZ we run 20 servers and about 350-400 desktops/laptops.

Late last year we completed migration of desktop/laptops to Windows 7 from XP. All laptops had been done about a year before that, but before the last stage of the migrations stated in October last year, we still had 200 XP machines running.

We still have about 10 servers running 2003. They don't do any DC or mail work, they do DNS and DHCP as well as hosting a SQL server each. They will be migrated early this year to Server 2008 R2
Our other servers are a mix of 2008R2 and 2012R2.
A couple of users have Surface Pro3 tablets, and they are connected to the domain and working OK, but we have no plans to roll out Win8 wider yet. Some of our Click-Once apps do not play nicely with it yet. I can see Win8 being skipped.