The game saves are Global and Ladder will be too - but you are not actually all one one single server.
Login goes through your Regional Authentication center then you are put on one of the datacenters attached to it. That is what determines your latency and games list for public games.
You can still chat with, and play with friends anywhere though - but if you join their game and they are 3000 miles away, your latency will increase.
This is only really an issue if you like public games and you are on a quiet datacenter or play at an odd time of day.
So far they have not released any info on exactly what the structure is or what IP addresses to use for WinMTR.
A Diablo 3 example, if it helps.
For Americas Region (which shares the same saves and ladder) in D3 there are 3 datacenters. California, Brazil, and Australia. You are defaulted to the closest one. BUT for D3 you can use a command line argument when launching the game to force it to a diff datacenter so you can have a different selection of public games.
So far no info on if that will be possible in D2R.