David Pogue has an interesting review of the MacBook Air in which he says:

Otherwise, though, I’ve lived and flown with this machine for a month, presented nine talks on it, and have not missed its missing features one iota. It’s plenty fast and capacious as a second machine.
Meanwhile, when your laptop has the thickness and feel of a legal pad and starts up with the speed of a PalmPilot, it ceases to be a traditional laptop. It becomes something you whip open and shut for quick lookups, something you check while you’re standing in line or at the airline counter, something you can use in places where hauling open a regular laptop (and waiting for it) would just be too much hassle.

What he does not say is that while regular MacBooks and MacBook Pros may be bulkier they also “start up with the speed of a PalmPilot”. I regularly pull out my 15″ MacBook Pro for these quick lookups, etc.