Well, I disagree with Neal Adams.  (wow.)  Tracing photographs is practice time.  And it's important to get the feel for reality that way, if that's how you want to go about learning to draw.  (life drawing is also a good idea.)  When it comes to actually drawing comics, it's time to use what you've learned, not trace people and draw costumes on them, getting paid for it and calling it your work.

There are rare exceptions.  Lightboxing is A-ok for times when it's impractical to do otherwise.  (Example, "Holy moley, I have to draw the White House and have it done in half an hour!")  Background stuff is cool.  But there's a limit, isn't there? 

Well, if he's saying the latter, then he didn't understand the question posed to him.  And it's an irrelevant point of view anyhow.  Who disagrees with the idea that tracing photographs in the privacy of your own home for your own edification is a good thing? 

The question is, should we all start tracing photographs that we didn't take ourselves, you know, out of magazines for example, lightbox them, alter them slightly and call it a comic book?

So rephrase the question to Neal that way, and see what he has to say.

People could draw before photographs, so obviously, that's not a given, but it's a very useful tool that can help an artist to evolve, and I assume that this is what he speaks of.. never say no to anything that can help you advance your understanding of the world.
Because it's not important how you eventually render it, in what style, etc, but how well you understand it at that time when you do.
For example, Jack Kirby clearly understood the world he lived in.
That fact shines through, even in images that often would not be regarded as "realistic" in any sense of the word.
It seems that Kirby was very "down to earth", and strangely enough I get that impression even when reading his most outrageous cosmic stuff.
(Goodland, not so much..)
I also belive this to be true with Spiderman, or any other truly powerful piece of storytelling and/or art.
It does'nt matter if you detail the world as a photorealistic rendering or surreal dreamworld,  if you have studied 'the real deal' extensivly and can relate that understanding, and phototracing is a helpful tool in regard to certain visual/architectural aspects of that process.
It helps me to get the general feel for cities, how they appear as a mass, and how buildings are structured, and how the mass of people flow within and through all of this.

It's a tool, and it's a good one, but eventually, you will gravity away from it, and rely more and more on your own powers of visualization.

Tracing is a tool of learning of how to get used to following the correct lines and getting yourself condition to draw things accurately. Many of the great masters DeVinci, Michaelangelo ,etc spent time tracing and copying other masters works.... If you don't know how to make the right line it helps you to make the right line...It is conditioning and learning how to see and how to make what you see appear on paper.

It wasn't a means to end it was a path to becoming a better artist. From that type of excercise you glean an understanding of how a particular artist goes about constructing things... I have found it a good excercise to break down an artist figure into its basic shapes and forms  and action lines to glean how a figure was constructed and how to then make it my own. Often  time you will see a pose or part of the body that you want to use and you have that as a reference point to help you out...

Looking at how artists spot blacks or setup the thrust of a panel or page is very insightful.... Kirby was a master of drawing your eye and then thrusting you smack dab in the middle of the action,... he did this with negative space and shadow and the thrust of the action..those elements are important to composition and to be able to break that down and see it  can only help...

Photos help you see things that you don't have access to in your imediate surroundings... If you have to draw an Elephant and don't have one in your backyard looking at photos helps you see what an Elephant looks like from different angles and you use that to help you create.

Matt, I think we all know -roughly- how the boddy fits together at least on a purely surface level. Fingernails go on the fingers...nose in the centre of the face, feet below the ankles etc.

"Knowing" your anatomy and skeletal layout is a very useful base from which to grow. But it doesn't do anything other than assist the artist with the translation, in the same way that understanding that knowing how to operate a cassette helps someone learn another language by listening to it.

Chris had wondered whether an artist has to train him/herself to "see" the world differently. That's definitely not the experience I have had, admitedly I'm only one person but I have mingled with fellow artisans over the years;-) The impression I get is that I already know how I see the world, the images spill out my ears everytime I look left and right before I cross the road! What I need to do is educate -you- how to see my images.

I do this over many years by learning how thing look when I make a mark on a piece of paper. I recognise what has worked for past masters and I develop those techniques my way. For example, Johns use of "Kirby Krackle". It's a technique obviously not of his own creation but he's developed this technique, subtely making it work within his artistic context so as not to look out of place. Yet we all understand what the Kirby Krackle is, we recognise it as breaking water, exploding stars, molten lava and the searing heat around flames when John uses it...yet boiled down they are only little circlis of black and white interlaced using the negative space to suggest form. We can all "draw" a full stop right!? The difference is that John has "persuaded" your eye to accept that this over sized full stop means something with the context in which it appears.

The good news is, we all speak Byrnese. The clever part is getting people to speak your language!