MBA is thin, but a little too thin. The MB and MBP are just right.
Besides that, I don't understand why people buy the MBA with what you can get inside. Do they just use them for small tasks? I dont see how MBA could run some of the more processor and graphics intensive tasks with out being slow.
I think we've all gotten pretty spoiled with the capabilities of some of these newer systems. I'm currently looking at upgrading my laptop from a 3 year old Thinkpad T60 running XP Pro. It has a whopping 1GB of RAM, a 60GB HD (of which I'm only using about 38 despite having used it for 3 years), and a 1.83 Ghz Core Duo with integrated crappy Intel graphics. I live on that machine, using it 8-12 hours a day for work, personal use, and some light gaming. I'm not a video editor, professional photographer, etc, but I do generally have 5-10 app and browser windows open, work with 200 page PowerPoint decks, huge Excel files, and a 10GB Mail folder. Honestly, the biggest bottleneck on that machine is the slow hard drive. Everything else about it has been fine, though the graphics card can't handle games that need 3D rendering, but it isn't built for that.
If you look at the specs of the machine I just described, which is the typcial business laptop in use by most companies today, the MBA Rev 2 has a slightly faster and newer Core Duo processor, twice the RAM, a better integrated graphics setup, and twice the HD space in a much faster SSD, weighs two pounds less, and gets about the same battery life (though you can't swap batteries). It's lacking a built-in CD drive, but I rarely use mine anyway, execpt to convince some games that I'm using a licenced copy. For me, especially as someone who is on 4-8 flights in a typical week, the MBA is a very attractive machine. The light weight and thin form factor make it a great machine for using on airplanes. The issue isn't the capabilities it comes with today, as much as it is how useful it will be in the future, especially the non-upgradable RAM. It's also expensive, but ultra-portables always are.
If you are into video editing, work with RAW photo images, or otherwise need a very high powered machine, I'd agree the Air isn't for you, but for a business user who travels, it's a great looking little machine.