I really should be doing real work, but since you asked . . . comparison of the new Macbook Air with the standard in ultraportables on the PC side, the Lenovo ThinkPad X61s. Both have full size keyboards. Both are lightweight. Both don't have optical drives.
Air, of course, runs OSX and can also run Windows vs. ThinkPad only able to run Windows
Air has a 13.3 inch screen capable of 1280 x 800 vs. ThinkPad 12 inch capable of 1024 x 768
Air has backlit illuminated keys vs. ThinkPad light that shines down, illuminating the keyboard (which doesn't work very well, I might add)
Air has iSight and microphone (and of course, the wonderful iChat video conferencing)
Air has LED screen (lower power consumption)
Air has gesture capable trackpad, though ThinkPad has that nubby eraser pointing device which I personally love
Air is thinner: dimensions: Air 12.8 x 8.94 x 0.16-0.76 | ThinkPad 10.5 x 8.3 x 0.8-1.1
Processor is the same speed, same type (al beit the Air has a modified, smaller Core 2 Duo)
ThinkPad can be configured to be almost 0.25 pounds LIGHTER than Air
ThinkPad can be configured with up to 4gB RAM, user upgradeable, instead of only 2gB
ThinkPad has unquestionably a better keyboard, but both are full sized
ThinkPad can be configured with faster and >2x larger hard drive--and it's user replaceable
ThinkPad has 3 USB ports, vs 1 for the Air.
ThinkPad has Firewire (aka 1394)
ThinkPad has built-in modem
ThinkPad has built-in Ethernet
ThinkPad has built-in cellular modem (X60 is Verizon and X61 is AT&T)
ThinkPad has user removable and replaceable battery
ThinkPad has available fingerprint reader
ThinkPad has available docking station
ThinkPad has built-in SD card slot
ThinkPad has built-in PCMCIA card slot
and again, with all that it's lighter!!
The innovation of aesthetics aside, I'm not so sure how innovative Air really is. But I do still really want one! For me, the thing that holds me back most is the lack of cellular modem. This seems an egregious oversight for something called the Air. I have signed up to the service on my ThinkPad, despite the outrageous monthly charge, and it is such a wonder to be able to be always on, with no need to find WiFi and no worries about the security of public networks.
(Probably things I've missed or got wrong. I welcome corrections.)