Over the weekend I was discussing the pros and cons of the MacBook Air with a bunch of other tech geeks and we came to the conclusion that the lack of an optical drive is a brave move of Apple's part (a move that other notebook manufacturers are likely to copy over the coming months), but that this could be the feature that's either the deal-maker or deal-breaker.
Bottom line, whether the MacBook Air is the notebook for you really comes down to whether you use the optical drive on your current notebook much. If you don't, then the living without one or buying the MacBook SuperDrive dongle might work out for you just fine, but if you're a regular user of that CD or DVD drive, then having to carry around an extra bit of kit doesn't make much sense. Not only are you lugging more kit about with you, a drive on a cable isn't all that suited to notebook user, especially if you have to use that notebook on your lap or in the car (I know, I've lugged external hard drives and ZIP drives around in the past).
I wouldn't be too worried about not having a built-in optical drive when I was at home or at the office (I already make extensive use of shared CD and DVD drives), but when on the move that changes. I can just see it now. All the cool of the MacBook Air (along with my smugness in owning one) evaporate as soon as someone asked me to read/rip/burn a disc and I'd be forced to pull our an "accessory" and hook it up.
Another concern that I have about the MacBook Air is battery life. Apple quotes it as 5 hours but in my experience Apple is always over-optimistic on such figures and my guess is that it'll be closer to 4 hours in real life (I'll let you know when I get my hands on one). I'm also willing to bet that battery life will plummet dramatically once you have added the drive.
Note: In fact, I wonder how many of the MacBook Air "innovations" (such as no optical drive, no Ethernet, and only one USB port) are down to battery life.
I think that it all comes down to what you expect from a notebook that costs upward of $1,800. For me, I feel that my dollars can buy me a lot more hardware if I don't want the Apple logo on it.