Only 2 more days before we find out! If they have a nice higher-resolution MacBook Air the same size as the 11.6" version, I just might be putting my 2011 on the Marketplace.
That said, if the new Airs still have lower-resolution screens, but there is a 13" MacBook/MacBook Pro with a Retina Display, I'd also give that a serious look, assuming it is the 18mm design with SSD. I can't see getting a 15" notebook ever.
There were a lot of interesting Ultrabooks announced this past week. While Apple has already ruled out touchscreens (which a LOT of the late 2012 designs appear to have), hopefully they saw the trend toward higher resolution screens and won't limit it to the Pro models. ASUS has a 1920x1080 screen available in an 11.6" design. That might well be enough to be called "Retina" if Apple crams one into the 11.6" Air.
If the new Airs are simply Ivy Bridge refreshes (presumably with USB 3.0 and 6Gbps SATA III SSDs), I might wait until the Haswell version next year. Either way, Haswell might bring a more radical exterior redesign, since the current unibody design will be about 3 years old by then.