Anandtech pieces together what processor Apple is using from Intel for the new MacBook Air, and concludes that Intel did provide Apple with a custom solution to be able to launch the thin laptop.
The CPU in the MacBook Air is a 65nm Merom based Core 2 Duo, with a 4MB L2 cache, 800MHz FSB and runs at either 1.6GHz or 1.8GHz. The packaging technology used for this CPU is what makes it unique; the CPU comes in a package that was originally reserved for mobile Penryn due out in the second half of 2008 with the Montevina SFF Centrino platform. Intel accelerated the introduction of the packaging technology specifically for Apple it seems.
The details of the processor technology may not be of interest to most, but that Intel would take special steps to accommodate Apple is interesting. In the past, Apple has previously gained early access to certain Intel processors for use in its Mac Pro.