Well I'am giving some work for my desktop CPU on daily basis. Let's say I'am watching Ace FHD stream, downloading in utorrent at high speeds (500Mbps total internet bandwidth, so ~10Mbps for Ace and what's left for ut) and browsing a website that has hundreds of gifs.
That would be 20-30% load for browsing
20-30% for Ace
~20% for utorrent
+ background stuff
so we are already on a combined 70%+ load for Q6600@3.3Ghz. The newest Air MIGHT be able to handle that, but it would result in very high temperatures (MBAs very easily climb to 90s C, not to mention the possible throttling), load fan noise and practically no reserve for futher demands, add to that inability to replace the components and it would mean that I would have to replace it with new model each year. Now on top of that, like I said, it's impossible to add any internal PCI devices to it, not to mention million other minor things like more ports, gigabit ethernet port, space for storage etc... so at the end of the day, like many people, there is no way I could use MBA as my main machine. Meaning specs for it aren't very important as long as it can handle basic tasks + 1 virtual machine.