No matter how snazzy an Apple tablet might look, after a few hours (or even minutes) with our fingers sliding all over it, we can imagine it taking a trip to smudge city. The fingerprint-resistant coating on the new iPhone 3GS seems to work well, so we hope it'll be used here as well.
A display measuring 10.1-inches diagonally seems to be the right balance of usability and portability. After all, it's the dominant screen size for Netbooks, so plenty of laptop users are already familiar with it. Most of these small displays are 1,024x600, but higher-resolution 1,366x768 versions are also available. We could see Apple offering the higher resolution as an extra-cost option.
Full OSX operating system
Most of the fake mock-ups of the Apple tablet we've seen so far make it look like a big iPod Touch, but that doesn't mean it should work like one. A touch-friendly full version of OSX would be infinitely more useful than a grown-up take on the iPhone/iPod Touch.
Our worst-case scenario fear is a closed-loop system with an officially sanctioned "App Store," and severely limited capability to install and run outside applications.
Mobile broadband capability
Wi-Fi is seemingly everywhere--until you actually need to use it (or it's behind some ridiculous pay and/or timed-usage wall, like at Starbucks). Apple doesn't currently offer built-in mobile broadband connections on any of its laptops, even though nearly every other major PC maker does.
However, Apple has done a great job of using that technology in the iPhone, so we have high hopes some kind of 3G hardware will be included, at least as an option. Also a possibility: a SIM card slot, something of a rarity (but not totally unheard of) on laptops.
An Intel Core 2 Duo CPU and Nvidia GeForce 9400 graphics
Nvidia's basic GeForce 9400 integrated graphics are a great value, and a big part of why we like the basic 13-inch MacBook models so much. Intel's essentially similar Ion graphics are coming to Netbooks in the near future, so we can't imagine an Apple tablet that couldn't keep up.
At the same time, many inexpensive laptops (such as this $649 Toshiba Satellite A505) have standard Intel Core 2 Duo processors, just like the MacBook line. Let's hope Apple sticks with that instead of the slower Atom-style CPUs found in Netbooks.
Plenty of ports and connections
If there's one thing we're willing to bet the farm on, it's that plenty of people will want to use the Apple tablet as their main computer. That will require a pile of third-party docking hardware and accessories, such as external keyboards, monitors, and optical drives.
A few USB 2.0 ports, an SD card slot, and maybe even an ExpressCard would go a long way toward making the device truly useful (plus, we think Apple has learned its lesson after the drubbing the MacBook Air got over its single USB port).