Generally, I prefer not to have alignment in my game systems. I find that alignment tends to detract more than it adds, particularly when the DM or game designer's take on Good/Evil, Humanity, whatever becomes objectively true, regardless of what the players believe. What I might consider an evil action, they player might not... or another DM might not.
A specific example: In ages past, I ran a game where a true neutral thief did not get along with the party's lawful neutral cleric. The player of the thief told me that he intended to let the dwarf walk into the next trap he detected without telling him to "teach him a lesson." I told him that was an evil act, and that if he carried on down that path his alignment would eventually change. The player argued with me over this. Later on, another DM told me that I was unfair to the player because it's not evil if you don't directly harm someone. Well, I believe that allowing harm to come to someone because of your deliberate inaction is, in fact, evil.
So...who's right? Well, we all think we are. The problem is that this kind of thing can have in game consequences; if someone had cast a detect evil spell on the thief when he was formulating his plan, I might have had it detect as evil intent. If it were a cleric or paladin and not a thief, I'd probably have taken away his spells until he atoned (if his character had actually gone through with it, that is) When alignment has game mechanics attached to it, players are essentially rewarded or penalized for conforming/not conforming to the interpretation of good/evil/whatever set down by the DM or game designer.
If we have to go that route, I almost prefer that the game designer, rather than the individual DM, set down the exact terms of the alignment system. Take a look at Vampire: the Masquerade (or Requiem...or actually any of the "new" White Wolf games) At Humanity 7, stealing triggers a degeneration roll, and so does anything that would trigger the lower Humanity levels. You might not agree that stealing is enough to push your Humanity down to 6, but at least there are no surprises, nor is there much room for argument.
If anything, I think OD&D and, strangely enough, 4th edition have better takes on alignment. OD&D takes good and evil out of the picture and replaces it with Law, Neutrality, and Chaos... those are, in my opinion, much less open to interpretation. More importantly, alignment had much less of an impact on the game as a whole. (Though often the game material seemed to treat Lawful as good and Chaotic as evil.) 4th edition, as far as I played it (which was about seven months), attached no particular mechanical importance to alignment, and it replaced the philosophically wonky Neutrality with simply being "Unaligned." I liked the idea that you could simply opt out of the alignment system. Now, I have no idea why they eliminated Chaotic Good and Lawful Evil, but as long as you keep those mechanics out of my hair, I don't really care.
The next time I run OD&D, I am also removing the alignment tongues, no matter what I do with alignment itself. I never liked that rule; even when I was ten I thought it was silly.
Warhammer Fantasy Roleplay, in it's 2nd edition, abandoned alignment entirely. I ran a campaign of that game last year and I have to say that the lack of a mechanical morality system, or even a non-mechanical system that simply identifies alignment, does not hamper the game in any way.
Here's an experiment I will likely never try: run Vampire without Humanity, or perhaps the only thing that causes a degenration role is the act of feeding from a living person. Characters might not be so cavalier about "filling up" before they go off to cause trouble, and because the idea that a vampire becomes more of a monster for stealing a car stereo is inane.