[rchowe]

The thing is, _every_ cocoa mac app currently uses the old UI classes, and it might be difficult to get existing mac developers to move to UIKit.

Typical Apple style is probably to move the UIKit stuff in for a release, then deprecate the old stuff in the next release (e.g. powerpc on snow leopard). Remember the Office 2010 apps that were being praised at the Apple event? Bam, deprecating the old UI APIs means that Microsoft has to re-code all of that to get their apps working again. And Adobe, not to mention all of Apple's apps, both internal and external. And devs can't target multiple versions of OS X.

The alternative that Apple is probably going to choose is to make the old UI stuff the new carbon - supported for a while, but not getting any updates. The real people this would hurt are, again big corporations, but some of the open-source projects who could spend their time on new features but are instead spending their time re-coding for the new UIKit APIs.