I think this is a great punishment. Think about it:
One of the major problems (IMO) with most MMORPGs are that dying really isn't that big of a deal. You lose a little gold maybe, or a little XP, or maybe your equipment deteriorates a bit. But generally speaking, it is by no means the worst thing in the world to die. This is especially true of seasoned players, because they generally have a group of people that will come and ressurect them, which in many MMORPGs allows you to come back to life withhout penalty. So how do you punish a PKer? If you kill him, it really isn't a big deal. This solution of cruicifixion is a perfect one. Because people who run around PKing are generally the types who spend 23hrs a day playing the game, crucifying a character for a few hrs will make it so that the person cannot play for several hours. This is a much worse punishment than simply dying!