I just ordered my 14" in my profile. When playing with a similar model at the Apple Store, I felt faster at opening apps and rendering webpages then my brothers Dell Inspiron 8600 / 1.4GHz Centrino / 512MB / 40GB 5400RPM / NVidia 5200 32MB. My brothers computers takes close to 20 seconds to launch iTunes, the iBook only like 5 or so.
Anybody know how the Centrino compares to the PowerPC G4??