IMHO the MBA is still quite a niche product, for ‘executive’ types that don’t do hard-core multimedia/audio/video work on the go;
I think by its preliminary measurements and technologies-namely the SSD option, hard-soldered RAM (ouch!), and 1.6/1.8 GHz proc., the MBA in its current state is too slow for most professional multimedia work; most audio/video editors, designers, etc., contend that even the ‘top rung’ MacBook Pros can only do some basic ‘cuts only’ editing, and basically do just that on plane trips or hotel rooms from gig-to-gig (my experience).
Now on to answering your question:
This wiki describes advantages/disadvantages for SSDs.
Since they are two different technologies, it’s difficult to measure performance on R.P.M.s alone-but ultimately the issues for comparison are speed, bandwidth (how much data throughput is possible-the width the data “pipeline”), and durability/power consumption/robustness each medium has.
I wouldn’t stake my claim on one of these puppies for my day-to-day work, but I guess if I were going ‘on vacation’ and needed to tote something beyond an iPhone, this could be a nice go-to option.