The new iBook is amazing, I finally got to hold one recently, but the weight bothered me. In Japan they are working on the sub three pound computer class. Take a look at The Sharp Mebius MT1. I think it’s just available in Japan.
What’s amazing is that it has a 12.1-inch screen and still weighs under three pounds. The keyboard retracts on closing to avoid damaging the screen like the TiBook. Of course, no DVD drive, but I’d be willing to give that up if Apple would make a lighter laptop.