I think we're going to see Xcode for Windows before we see iOS running on Macs. In other words, I wouldn't be surprised if there was no more Mac in five years.
So, I know Apple is making a lot of money off of iPods, iPads, and iPhones, but they still had 33% year-over-year growth in Mac sales last quarter.
I don't think the Mac is going anywhere soon. I do think we'll see substantially changes to Cocoa with a lot of things (coughbindingscough) being effectively deprecated in 10.7. I expect the next revision of AppKit to look a lot more like UIKit.
