RP servers, at least in the open beta, use normal rules for PvP, meaning you are not automatically flagged for PvP in contested zones (Redridge, Hillsbrad, Stranglethorn; any area level 20 and over). You are basically free to do whatever you want without distraction from the horde unless you enter PvP.
What it means is if you see a horde walking by, you can't attack them. Not very realistic from an RP standpoint in my opinion. As many have said, PvP can be a whole lot more fun than the normal servers.
Ganking, I think, will not be as bad as it sounds. If we do choose an RP server with PvP rules, that will already eliminate a lot of the immaturity that is associated with gankers. Personally, I think it is also a bit more realistic from an RP standpoint: If you see a horde walking by, you will want to attack him or her since horde and alliance are enemies.
The more I think about it, the more I want a PvP RP server.