I'm thinking about buying an Air as well and was hoping for some advice.
I've got an iMac that I'm currently using as my main computer and a MacBook that I use as a secondary machine (I travel with it, take it to class and work, etc.). While the MacBook is nice, I'm really envying the size and weight of the Air.
My main concern here is price. I keep very little on the hard drive of my current MacBook (I use Simplify for music and my iDisk for any files). I only use it for web browsing, word processing, and OCCASIONALLY statistical analysis (using Stata). I would be perfectly fine with a Rev. A, B, or C. Again, whichever I can get the cheapest.
All that being said: how much can I expect to pay? Does anyone have any suggestions on where to get it? How much could I sell my MacBook for? (It's an original 2.0 GHZ unibody MacBook with 4 GB of RAM and AppleCare through October 2011).
If I were you, I would sell the MB, and use the money to get a rev B/C MBA from Apple.com refurbished. You can get the rev B 1.86 GHz with SSD for $1349. You can get rev C 2.13 with SSD for $1549.
The absolute CRITICAL part is to get B/C with the Nvidia GPU and Penryn CPU with SATA-II drive controller.
The SECOND MOST CRITICAL part for an exemplary experience is to get the SSD version. The HDD in the MBA is 4200 rpm which is rather slow. Most people used to think of upgrading their HDD as best way to improve performance but that was 5400 rpm to 7200 rpm. The SSD is effectively taking it to 5x to 10x the performance of HDD.
I would prefer a rev B/C with Nvidia GPU and HDD to ANY original MBA even with SSD. I would prefer a B with SSD to EITHER a rev B/C with HDD.
Last most important feature is the clock speed of CPU between B/C. However, when thinking long-term most HD video playback programs like iTunes recommend 2 GHz. At the same time, I played HD fine on my 1.86 GHz rev B. Consider though that 1.6 GHz may be too slow a few years down the road for a lot of apps.
I think you would be happy with your MBA for a long long time if you buy a 2.13 GHz rev C with SSD. At $1549 it would be like new and include a one-year warranty. You could extend it out many years if you wanted.
Finally, I see no reason why you couldn't sell both of your current Macs, buy a rev C 2.13 GHz MBA with SSD for $1549, and an 24" LED ACD for $599. Throw in the MBA SuperDrive, MobileME, and a Time Capsule, and you're setup with the ultimate Mac user experience. It's the setup I have, and it will be far superior to a two computer system. I absolutely LOVE my Mac setup. I would never go back to two computers, as the Nvidia 9400m drives the 24" LED ACD amazingly. If feels like a Mac Pro to me (will not if have HDD), as the SSD really makes up for slower other components.
I have fallen hard and fast for my Mac setup. I recommend it to many people, and I cannot say how many people have PM'd me stating they bought the MBA with SSD and LOVE it. Then they buy the 24" LED ACD and again LOVE it. Most end up selling their iMacs as they realize the LED display is better and the MBA is faster than their iMac ever was.
Good luck.