Thanks all for your responses on this! It definitely satisfied my speculation habit, just couldn't respond earlier because of lack of Internet access.
It would be incredibely hard to use if it was as thin as a piece of paper. I like my gadgets to have some sort of weight to them, it gives some substance and makes it fulfilling to use them.
I sympathize with this view, but I think it originates in the fact that we just don't know what it will be like to use an iPad that's thinner and lighter than what the current model offers. For one, the lightest tech we use is usually made out of cheap materials (i.e. plastic, like the Kindle), and thinner items tend to be hard to grip. But will a future iPad that's significantly thinner and lighter feel cheap or hard to hold onto? I don't think Apple would put something out like that.
Maybe it would help to think about the latest iPod Touch and the MBA in this regard. The fourth gen of the iPod Touch was thought by some to be too thin and too hard to hold onto. I have the latest model, having upgraded from the second generation. At first I had the same impression of the fourth generation, but now that I'm used to it, I find it to be just fine (haven't dropped it yet!). The design of the new iPod Touch is already embedded into the new iPad model, but I can't see the iPad getting that much thinner without it being difficult to use, as you say. (The iPhone, on the other hand, I would hope stays roughly the same in its form factor. I could see thinner models easily falling out of people's hands. Using the iPod Touch as a phone is not that great on the hands - feels sharp when gripped like a phone, and also feels liable to be dropped. Other hand positions on the iPod Touch aren't that bad, though.)
The MBA on the other hand can get as thin and as light as possible and I don't think it will ever feel cheap or difficult to handle. Granted that it is not a mobile device like the iOS devices, so criteria for judging is quite different.
This is what the different components weigh, you decide.
Aluminum back 138g / .3#s
Battery 148g / .33#s
LCD 153g / .38#s
Glass (and frame) 193g / .43#s
Speaker: 17g / .04#s
Main board: 21g / .05#s
Everything else: 27g / .06#s
Thanks so much for listing these! I suppose you wouldn't know how the aluminum back compares to a back out of LiquidMetal or some other potential material (carbon-fiber?)?
Outside the Star Wars saga, I'm pretty sure carbonite doesn't exist, at least not yet.
As far as using carbon fiber? There are bike frames made from carbon fiber. It's lighter weight, but to maintain the strength, the material is somewhat thicker. Even so, carbon fiber can (and does) crack/break. Once a carbon fiber frame is damaged, it can not be repaired and safely ridden.
High quality carbon fiber is also extremely expensive. I have racing wheels with carbon fiber rims. I only use that wheelset for racing though because aside from the risk of damage, that wheelset costs $1,600, and that's not including the tires. For training and pleasure, I use an aluminum wheelset, which still cost more than the starting price of an iPad, and it's a little heavier, but far more durable. Carbon fiber is also susceptable to UV sun damage, and is considered to have a "finite life" which probably wouldn't be relevant to it's use in an iPad.
Carbon fiber doesn't have much "give" but also has superior shock absorption, so it might make a fairly suitable replacement, providing it could be produced cheaply and thinly enough.
There's probably greater potential for weight reduction in the screens and batteries.
Thanks for this lengthy post on the carbon fiber option. Not sure what I was thinking when I mentioned carbonite! I was probably trying to remember the name of LiquidMetal, which is another material in the running to replace aluminum on some Apple products (or maybe just the glass back on the iPhone?). I know about the cracks in the carbon fiber frames for bikes... but I imagine any carbon fiber used for an iPad would be under much less stress than a bike! And I don't think sun exposure would be that much of an issue, for the same reason (different products, different uses). Thanks again, though, for your input on the potential benefits and drawbacks of carbon fiber.
