The Air is in a completely different league to netbooks, for a number of reasons. Even the slower CPUs in the 11-incher are 30-60% faster than comparable Atom parts, but consume 30% less power. CPU performance of the 11-inch model is comparable to the 2006 Macbooks and the 13-incher to the 2007/2008 Macbooks.

The big performance story is the GPU and SSD.

For the majority of Air buyers, their new machine will feel quicker than any computer they've every used, by simple merit of the SSD. Cold boot times of 15 seconds are being reported and programs will load with similar haste.

The GPU is a big deal, both for graphics performance and OpenCL. OS X has always leaned heavily on the GPU. With the introduction of Snow Leopard, the vast floating point performance of the GPU is available to the whole system. If you've been following the Folding@Home project, you'll know how big a deal that is. Of course third-party developers are proving fairly slow to make use of it, I will bet lumps of my own flesh that iLife 11 will be heavily optimised for OpenCL.

We've already mostly dispatched with the megahertz myth, but we're going to have to confront the idea that CPU speed is a relatively minor part of real-world computer performance. The old Air felt miserably slow, mainly due to hard drive throughput. The new one will feel very fast indeed, in spite of a relatively modest CPU.