I finally had time to actually use the Air. A few thoughts...
Second Life works tremendously better on the Mac side and there is no lag.
The VGA-out dongle worked fine. On the Windows side, you need to use the Intel mirroring software and on the Mac side you have to set the screens to mirror. By the way, the native resolution of the Macbook Air is the same as the Macbook @ 1280x800.
Below you will find two photos of the thickness/thinness factor of the Macbook Air. Clockwise, the items are the Macbook Air, the Fujitsu P1510D tablet, the XO, an iPod Touch, a Treo 700wx, and the Asus eeePC.