I might be a newb to this forum, but have been using and following macs for well over a decade. (remember, back when laptops looked like toilet lids, and were roughly as useful too)
Anyway, given the consensus around here about what the new MBAs will do and contain (moderate to good speed bump, possibly more ram, lion preinstalled, TB enabled, worse graphics), i think they will NOT define or change anything, unless apple decides to really surprise us price wise.
Provided they cost more or less as much as the current ones, they will still cost more than PC equivalents, enough to make the majority of regular consumers choose a PC.
Now if Apple decided to drop the "apple tax" just this once, it might change something (Apple is now one of the worlds biggest companies, and IMO, the essence of their success is getting people to voluntarily pay the premium.)
Even if they did it would not change computing in the way that iPhone and iPad did.
I almost never see a businessman/woman without an ipad anymore, and myself I just can not see how I can live without an iPhone.
Even though I really REALLY want one, I can live without the new Macbook Air.