Apple made it pretty clear in the announcements that this was designed for the business traveller. 95% of the people who visit MacRumors do NOT fit into this category. However if you were to sell this thing only in Northern California it would be one of Apple's best sellers.
A business traveller to me is somebody who flies at least twice a month and is on the road all the time.
But so many of the design choices that went in to the MacBook make it a lousy computer for business travel.
One thing about travel, is you need to be prepared for uncertainty.
You might be stuck in an airport where free outlets are hard to find (especially if there's a flight delay, and hundreds of passengers are crowding around the few available plugs to charge their phones). That means you NEED long battery life and/or the ability to quickly swap in a spare battery.
You will sometimes find yourself in places were there is no Wi-Fi signal, or it's prohibitively expensive, or it's so weak that it's nearly useless. Most laptop owners can keep an ultra-thin retractable Ethernet cable handy for such situations. MacBook Air owners must also carry a USB network adapter dongle, and (as it turns out) a USB extension cable because no adapter on the market can fit into the Apple USB port!
You may occasionally get handed something from a customer, client, boss, etc., on CD or DVD and be expected to work with it. A business traveller with a MacBook Air will have to wait until they get back to the office to do so, unless they bring an external drive along.
With a length (and open height) that is nearly the same as any other MacBook, it will suck to be you if you find yourself flying coach (which does occasionally happen) and the person in front of you decides to recline their seat when you're trying to work or watch a movie.
Need to pee when you're alone in a coffee house in a distant city? Better take the MBA into the john with you, because there's no way to lock it to the furniture while you're gone.
All this for $1800.
If the "business traveller" market really is what they are counting on to sell this thing, it's going to make the Cube look like a massive hit in comparison.