The verdict? I give it an A, and on a good day, an A+. It's a very simple design: a plastic sleeve with a hollow plastic plunger that is tipped with a tight-fitting rubber tip. You screw a mesh lid onto the sleeve, insert a paper filter (these are reusable, but they're also tiny and cheap, and you get 350 of them with your Aeropress), and pile dry espresso grounds on top of the filter, and rest the whole thing on a sturdy cup or mug. Then you add a measured amount of 175°F water, stir for 10 seconds, and gently but forcefully depress the plunger. The espresso that emerged was uniformly delicious -- sweet, dark, and without a hint of bitterness.
The theory behind the Aeropress is that you can get a better shot of espresso if you extract your coffee quickly, and at low temperatures. In order to do that, you need to really get the water into contact with the fine-ground coffee (hence the stirring step), so that you get a nice shot even without a lot of heat or time.
This is not without its drawbacks: I never managed to get any crema onto any of my shots (looking at Aeropress message boards, I can see I'm not alone). Also, the shots that the Aeropress delivered were really short -- I found myself increasing the amount of water about one third above their recommended levels. Finally, the business of getting your water to 175 Fahrenheit is very fiddly (I used a $6 meat thermometer from Canadian Tire and clipped it to the mouth of the electric kettle). What's more, the Aeropress comes with a couple of largely useless accessories (a funnel and a stand for the filters), but omits the absolutely vital thermometer, which seems ill-considered.
But the disadvantages are vastly outweighed by the advantages. As I said, the coffee is great (everyone who visited us or vice versa got a shot or two, most asked for seconds). The cleanup is really simple: the piston scours the sleeve clean of all grounds and oils, so all it wants is a rinse at the tip when you're done. And the setup is compact, portable, and requires no electricity (though you need some means of heating water). We combined it with a microwaved milk frothed with a little battery-powered whizzer, which was no substitute for properly frothed milk, but beat most chain-store milky espresso drinks hands down.
At $30, the device is a very cheap way of making espresso, and despite the thermometer fiddling, I found it much easier to use than my traditional steam-driven machine in my kitchen. If you're trying it out, pay close attention to the instruction not to press too hard on the piston: just push in an inch or two, wait while the water permeates the grounds, then push the rest of the way in.
I've put my Aeropress in my permanent travel kit.