I would say go for the SSD drive if you get the Air because the standard drive is only PATA and not SATA which is much slower. But if you do, it will cost well over $3000, which is why the MacBook Pro is a much better option.
Supposedly they're something like 100x faster than a hard drive.
Ah well the MBP has a 7200 rpm drive, I think (opposed to 4200).
So it really is just proportional to the difference in RPM speed? There isn't any additional (significant) difference arising out of PATA vs. SATA?
Not just the rotational speed - the smaller the platter is, the less data passes under the heads in one rotation (the track length, therefore the amount of data bits, is the perimeter of the platter. Smaller platter = shorter track length)
I could make up a bunch of numbers too. You're assuming a lot (price, time, the hard drives in MBAs not being able to be swapped with SSDs by an Apple Tech, the speed difference actually mattering to the person, etc...)
Is there any reason to think that an Apple Tech couldn't swap out the 4200 for an SSD down the road?