The processor is BRAND new! It was developed specifically for Apple's product!
The package for the processor was developed "for" Apple's Macbook Air. The actual CPU core is not custom, only the package the core sits on (the piece of PCB and the pin-out and whatnot).
Also... This new packaging appears to have been created by Intel not just for Apple, but also for their upcoming Montevina SFF platform due in the second half of 2008. Montevina is the successor to the current Santa Rosa mobile platform (the platform is the whole package -- CPU, chipset, and CPU packaging, among other details -- the codename for what Intel markets as "Centrino"). Intel intends to release at some unannounced point after Montevina ships a special Small Form Factor (SFF) version of the regular Montevina chipset.
Anand published an article today, which makes a lot of sense, postulating that Intel already had developed a core-compatible new SFF package for their upcoming new SFF platform which will be issued in (probably late) 2H 2008. Likely what happened went something like this:
Intel: Hey Apple! We hear you're thinking about doing an ultra-portable (and you have that Mac Mini and Apple TV box that desperately needs an update). We have some cool new stuff coming up in late 2008 you might be interested in. The CPU is on this nifty new package that is 60% smaller than the ones we currently use for our mobile platform CPUs.
Apple: Wow, cool! We actually have a product in the pipeline that this'd be perfect for, but it is due out way before the end of 2008.
Intel: Oh, that kinda stinks.
Apple: Yeah. Hey... Any chance you could hook us up with a special version of one of your current processors on that fancy new package? We're going to seal the case of the box, so the customer won't be able to open it up and upgrade the CPU anyway, so it doesn't matter if it doesn't use the standard CPU socket! And, besides, we're "cool" and we'll pimp you up when we announce the product, and tell them how cool you were about it.
Intel: I'm not sure... Let me check with the engineers...
Apple: (tapping foot)
Intel Engineers: (grumble, grumble)
Intel: They said they can swing it. We'll hook you up with one of our current Merom CPUs with the fancy new package for your cool Macbook
Thin Air. Make sure to pimp us hard in the intro though. In fact, Paul wants to go out on stage, and wants some cool free Apple swag for his kids.
Apple: No problemo! You guys rock! Why did we dis you so hard for so long?!? Screw Motorola and IMB!