One of the talkers on Mac Break Weekly (#145 06-16-09) swore by the Air as his de facto traveling companion.
On the other hand, I've seen some posts that seem to imply that some battery packs may not be "compatible", to the same degree that some charger cables might cause the 3G(S) to complain about a non-compatible accessory.
Here's a YouTube unboxing review by . He has other reviews (IIRC) comparing it to the Incase Power Slider.
Same here. I've read and read and read until my eyes have bled about these cases, more so on the Air than the slider. But I agree that most of the reviews fell in the 3 out of 5 range because reports of signal loss which I believe is to be true if you are in a low coverage area rather than an area where signal is very strong. Another complaint is that the top piece can snap too easily if you're not careful taking it off to put the phone in or take it out of the case. Seems the top is made of thin plastic in places around the access holes so be careful if you're going to be taking it on and off a lot.
You can order more cables and actually more top pieces from the mophie site if you need extras.
don't like the USB connector or the fact that the AIr is a fingerprint magnet. Likes the 2G version's surface. Want an Apple connector on the bottom. I have a dock extender and am able to dock the phone regardless of the case. But with the air...I have to have a dangling wire on my desk to charge. I got an 1800 mah battery charger on ebay for $18 and this works in a pinch.