After playing many years on a PvE server, a RL friend and I rolled toons on a PvP server. He rolled an UD Warrior, and I rolled a Tauren Druid healbot. I played a Hunter, Priest and Warrior to level 20 before deciding druid was for me. I absolutely am loving a druid on a PvP server. I am currently at level 40 and showing no signs of slowing down.
I stealth around with my Warrior friend with track humanoids on to give warning to any ally incoming, and if my friend gets ganked, it's healbot go!
When we have to solo, he gets ganked a lot.
As for me, I can be in stealth mode, make sure no ally's are near, kill my mobs, and get right back into stealth mode. Only been jumped a handful of time. (darn stealthy rogues)
You also can't really put a price on needing a mob in the end of a cave, hitting that stealth, and avoiding many time consuming mobs. It really sucks working your way nearly to the end of the cave, only to get ganked and having your mob stolen.
So in my personal experience, druids seriously kick *** on PvP server.