I currently play on 3 different servers.
To give you a frame of reference they are as follows:
Server A
This is the server I first played on, and which houses the majority of my characters. It is a PvE server, and my 70 horde Druid and Warlock are here.
Server B
This is a PvP server I rolled on after many months on server A. It houses my NE Druid, and several other lower levels (including a 35 hunter and 32 priest).
Server C
This is a PvE server that I rolled on recently with a friend. It is the home to my current main (40 BE Paladin) and also a 19 UD Rogue alt.