Player vs. Player combat has become a point of contention on the SWG developer boards for quite a while.
Success with PvP systems has been mixed when considering MMORPG releases to date. SWG plans to take a different avenue than it's predecsors. I wonder if it's enough to bridge the gap between these two opposing points of view.
What kind of player are you? Do you want a more realistic environment where players are fair game for attack or would you rather not have to watch your back at every turn, wondering if someone is going to take you out?
I think SWG's system is really great. It doesn't prohibit it (ie, it can happen almost anywhere), but those who don't want to participate probably won't (they can make their attackers outcast). If you want to participate, you declare to a faction or join a PA that is at war. I hear some quests will also involve PvP.
Voluntary is the key idea.