In anticipation of the Air's arrival, I said the following:
For me, the Air will be a secondary machine -- a complement to a blazing-fast Mac Pro -- and that, I think, is how it's being positioned (if not explicitly); indeed, the dearth of ports almost demands the conclusion.
That equation has changed a bit for me since taking delivery of the Air a month and a half ago. I now think that, given enough time, the Air will become my primary, and indeed only computer.
This revelation is informed mostly by how little I've used the Mac Pro since the Air came into my life; and when I say "little," I mean only a handful of times, and even then only for Lightroom and Photoshop. While I don't think I would like using the current Air for the sometimes complex and processor-intensive stuff I do with those applications (and I'll admit I haven't tried), something tells me that two or three revisions from now, the Air will be wholly sufficient for all of my needs (and surely it's presently adequate for most everyone else).
Relatedly, and unsurprisingly to me, I've yet to use any of the available peripheral ports, much less need any of the ports it doesn't have.