First of all, let me say that I think this is an achievement in making something thin. I can't take that away from Apple.
But I am an independent Apple certified technician and I look at the MBA not as a user, but as someone who will have to repair it for a user (software repairs only, of course. Hardware repairs will have to be sent to Apple due to warranty).
The lack of both a firewire port and an optical drive will make this a little more difficult to troubleshoot and repair. Sure, I can pack my own external out onsite, and even boot to my usb hard drive, so it's not horrible, but I'm afraid that many people who buy this are not going to know what they're missing until they need it. This is truly going to be a "depot repair" computer in that any hardware issue will need to go back to Apple to have repaired. That will make a difference in places where I am (literally) the only Apple tech for 100 miles.
Also, the supposed target group for this machine is the same group (generally in my experience) who isn't going to know how to set up remote disk to install software, or have a N router to get the full benefit of the wireless on this machine (yes, I know it works on other wireless networks). There's a lot of people who may buy this as their primary computer that are really going to be turned off by how much setup they might need. And you can be reasonably assured that the customers won't be told all of these things before they buy it (but that's the same with electronics in general, so I'm not bagging on Apple for that flaw).
This one also really defeats the "ready out of the box" idea that Apple has courted the last couple of years, because this one really isn't ready out of the box, like most people think that it will be.
So, for what it's worth, that's my two cents. I think it's an interesting idea and that it does have some market, but I'm still not sold that it's a good idea.
EDITED: Another thing I'm interested in is if the MBA can bootcamp windows? Could you install Windows using a wireless remote disk? That might actually necessitate the need for an optical drive. The only reason I ask is because that has been another of Apple's selling points the last few years. This might take away from some of it's usefulness if it's a pain in the ass to install windows onto.
Also, if the optical drive is dead why can't you download Leopard? (maybe you can and I just don't know about it.)