... my evolving thoughts on this matter, and conclusion!

I'm really impressed by what people have had to say so far.

everyone!
I knew at the outset that character alignment, a being's "moral code", as many may say, is obviously a victim of our personal perceptions. Semantic problems also intrude into the issue, and that really reflects our real-world situation! I don't know about you folks, but I game to escape. Even an imaginary world where I can play a character with special advantages, rather than mundane traits, to conquer real-world problems is an escape of itself. (Magic, super powers, privileged knowledge, etc.) I like to escape from the arguments too. But sometimes that's hard to do...
My initial thoughts:
Morality covers very deep philosophical territory--despite the simplistic child-like black hat vs. white hat mentality typical to our present day media, politics, entertainment, and popular culture. Likewise, I think D&D, especially in editions past, handled it just as poorly... Thus, I'd go out on a limb and say: character alignment, as designed and expressed in D&D, is for kids. As an adult gamer, I don't really need it to enjoy a good adventure. I'd rather delegate alignment to the nebulous goings-on in a setting that our PCs are exploring. If character alignment never existed in D&D, would it have really changed our enjoyment of the game? Couldn't a paladin still have a profound code and special abilities without the LG label to "quantify" his/her moral character! A code of conduct is a logical concept--an over-moralizing label is something else altogether. I know that we are supposed to use fair judgment in handling alignment. But the concept seemed to undermine character development by limiting behaviour to a mere category. Or even worse, limiting a character's conduct to a categorical imperative, i.e.: LG behaves precisely THIS way, CE behaves exactly THAT way, ad nauseum.

Is that really necessary? Do we really need some game publisher to provide for us definitions and labels for PC behaviour? May I not play a character that struggles with moral issues without being pigeonholed? How many of us have interpreted alignment in D&D this way?
Well, I found some answers by rereading the beginning of Chapter 6 in the PH. (I should've reviewed Chapter 6 before posting the poll. My bad.):
Right-off-the-bat the alignments are meant to be viewed as actual forces in the D&D multiverse, NOT philosophical concepts! (Okay. But I thought they were meant to be your PC's moral and personal attitudes?) Probably overlooked by many from PH page 87, lower right column: "Alignment is a tool for developing your character's identity. It is not a straitjacket for restricting your character. Each alignment represents a broad range of personality types or personal philosophies (I thought it was said they were actual forces and not... what a contradiction!), so two lawful good characters can be quite different from each other. In addition, few people are consistent." Not even day to day! (Neither were the editors of the PH!

) "Good people can lose their tempers, neutrals may be inspired to perform noble acts, and so on." Additionally, on PH page 89, upper left column: "Use these descriptions as guidelines, not as scripts." As Henry here stated quite well earlier on: they describe your PC's personality, they don't prescribe your PC's personality. (Aside: how many of us have read specific sections & tables of the PH, and thought that was enough given past experience with earlier editions of D&D through reading and playing with friends? Sometimes rereading rules you'll catch things today that you missed 6 months ago! This is true of many things in life, no?)
As alignment concerns character behaviour, the terms "should" and "shall", as well as "would" and "will", are often used by D&Ders with respect to anticipating a PC's or monster's behaviour. Trouble is, these terms toss us directly into the quagmire of semantic debate, as the meaning of these terms are not precise given conventional usage these days--look at your dictionary, I have--and much fuss is made about commandments, directives, determination and obligations implied by these words. Does LG mean your PC "shall" or "will" or "should" or "would" behave a certain way (your choice?

)
Oh, forget THAT. Getting bogged down in semantics is what spoils my enjoyment of what supposed to be a game, a recreation, and an imaginative and escapist pastime. Debating the semantics (the meaning--for the kids here) of terms may be interesting--but NOT in the middle of my gaming session! I don't appreciate table arguments as a player, and especially not as a DM!
So, my thoughts have changed:
Indeed, it seems more practical, if not entirely logical, to judge moral character upon past conduct and not potential conduct! That is, alignment represents one's behavioural history, NOT one's behavioural intent! At most it is a predictor, but... "The future is uncertain..." Yoda, ESB. Thus, it's simply a matter of saying to oneself: "My PC has grown up to be NG, he/she may change, but he/she is currently NG." At the least you have something to work with in developing your PC, and can continue the PC's current alignment as a "trend" or "plan". Adventuring may change your PC's alignment, but that's potentially a really cool thing...
Gawd, that makes things MUCH easier! It also may help with the next concept:
I, like many whom have posted here, prefer the idea of tagging only outsiders with an alignment as a genuine qualifier. It makes sense to me as they represent the immortal epitomes of Evil, Good, Chaos, Law and maybe even Neutrality (?). Of course a fair amount of arcane and divine magic spells are likewise tagged to mechanically interact with these powerful beings who are opponents and obstacles. That works well I think. So now, theses forces, expressed by the DM's campaign, may be defined as vying for your PC's moral development! And lo, we come back to the initial game designer's definition; the deities (and their minions) are themselves representatives of the alignments as forces (and not just figment of someone's philosophical rantings

).
In summary, alignment in D&D may be clarified as follows:
Alignment, for intelligent mortals, reflects an accumulation of past conduct-almost a karmic aura, or taint, or stain on a mortal being. Such conduct may be a result of personal choice, social conditioning, or coercion. But the mortal is not locked into it. A mortal's alignment may change, even a humanoid's... Half-Orc Paladins! Yay! 
(Okay. Lots of fall-from-grace and rise-to-redemption fodder. Typical of the dramatic material from the classics like Shakespeare (not always a happy ending), to the cheesy Hollywood blockbusters (always a nauseating happy ending, despite the drama and destruction. The D&D movie anyone? That was so bad, on so many levels... Oh the shame of it...).)
An alignment is a "real" force, typically manifested as immortal entities (outsiders), attempting to manipulate the mortal world(s). Alignment, as a genuine, defining thing in the D&D multiverse, is subject to divine and arcane magic, psionics, and special abilities that actually interact to aid, deflect or thwart it. So defined, powers affecting alignment are limited to affecting outsiders and their agents. (The core rules
do corroborate this!)
Not perfect but close. It works for me, avoids most predictive arguments, leaves choices for players, and revises my initial answer to my question: is alignment essential to the D&D experience?
Yes, but not insufferably so. One could do without alignment, but an important component of what defines D&D, a staple of the fantasy genre, would be lost: the interactions between the mortal world & the immortals beyond... (GURPS fantasy never satisfied me in this regard!)
Of course many may still disagree with me, but the above is my conclusion for now.
Thanks to all for sharing your thoughts thus far!
-Winterthorn
PS: Hey, this was my first poll! Not bad, eh?
*pats himself on the back*
Next time, though, I'll try to ensure the poll options are more concise. A little pre-poll research may be required too--we'll see. *shrug*
