I've read quite a bit of speculation lately about the Apple Tablet. For some background reading, try John Gruber, John Siracusa, and Marco Arment; or, on the skeptical side, Joe Wilcox—who I'll start with. I don't usually make predictions like this, but I feel like I've got a good handle on this one so I'll jump out on a limb.
Wilcox points out "that the company [Apple]'s most successful products pushed into established markets, even if marginally created." The iPod joined the universe of portable audio players and the moribund market for mp3 players. There were billions of cell phones before the iPhone, and "smartphones" were already a recognized category. Tablet computers, by contrast, are few and far between; a "niche category" for which there's little market.
But he's missing the point. Apple products aren't (contrary to popular belief) defined by what they look like, but what they do. An "Apple Tablet" won't be a tablet computer, it'll be a computer that is a tablet. The market they're probably aiming at is regarded by many as quite vital: netbooks. Specifically, this is aimed straight at Chrome OS.
Gruber goes on in some detail about how he thinks the product will be transformative; I suspect he's mostly right. Google (and others plan to build netbooks/tablets that are based entirely on the browser. An Apple netbook building on the CocoaTouch community offers a great deal beyond "just" web functionality without sacrificing the simplicity of something like the iPhone OS (or Chrome OS). It can be a netbook, an eBook reader, a portable video player, and anything else an enterprising software programmer can think up, all in one device—indeed, as the iPhone already almost is.
To me, there's two big ifs. The first is 3G support: If Apple could snag the sort of internet anywhere deal the Kindle has, that'd be amazing, but even with a monthly plan it would be an impressive offering. Let's hope it can work off AT&T's network, though. If the iPhone alone is bringing them to their knees I'd hate to think what this might do.
The second is data entry. The likeliest method for this is an onscreen keyboard, but that still seems fundamentally inelegant for a tablet, which (unlike an iPhone) would probably be too large to comfortably hold and type on at the same time. Apple's had Inkwell sitting in the closet of OS X for a long time now. Maybe they'll ship it with a stylus? Or maybe I'm just too fond of handwriting.
Anyhow, that's my two cents. Thanks for reading.