This has been discussed before and we are undecided. If we play on a pvp server, we will end up being a roleplaying pk guild. Unless they have an RP pvp server.. Also, we do not know how PvP will work on the regular servers yet. The regular ones will have more RP value than just running around and ganking people. There will be objectives to complete, towns to take over. Example, you could come into a town, kill all the NPCs and Quest NPCs and basically take that town over. Perhaps even kill the travel NPCs so people will have to run there to destroy us.
As of right now I am against a pure 100% PvP server. I would rather like to see a DAoC setup. Certain zones that are for PvP.. which WoW will have... but I just hope those zones are not tiny. DAoC had quite a bit of freedom in running around. DAoC also had the battlezones where you could take over the central keep. Except in WoW, there will be consequences to the other side when you take over something (killing of quest NPCs), or there will be a reward, like a super powerful weapon, or gold, etc.