Since Apple announced WWDC, there has been some panic over the Mac platform disappearing or becoming obsolete or a second-rate citizen, or whatever. All this springs from the fact that there are no ADAs listed on Apple's website for the Mac; it only mentions the iPad and iPhone platforms.
Mac OS X isn't going anywhere. Apple's just trying to reshape the computer market, and we don't like it because we've invested a lot of time and energy into the Mac. But whether we like it or not, the Mac is not the most optimal consumer experience for 90% of people out there; the iPad and iPhone in conjunction do a great job handling most tasks we need to accomplish on a regular basis.
The Mac is still a perfectly viable platform for professional-grade applications, and it will remain so for a while to come, I imagine. People still need it for editing photos, creating professional videos, editing music, etc. There's plenty it can do that will never be suitable for a closed platform like the iPad. (Another great, relevant example is Xcode. There will probably never be one on the iPad, only on the Mac.) But for the rest of us, using the Mac is overkill. You don't need a whole laptop just to "check your internet" and maybe write a blog post or tweet. You don't need it to make purchases on ebay or to fire off an email to your buddy across the pond. The iPhone and iPad let you do these just fine.
Some developers have also conjectured about AppKit being deprecated and UIKit being "back-ported" to the Mac. This isn't going to happen. UIKit is based on touch, and AppKit is based on mouse/keyboard interaction. They're 2 different worlds. The only way this would happen is if Apple decides to make a version of their Macbooks that has touch capabilities.. and if they did that, well, they would probably want to get rid of the keyboard... see where I'm going with this?
Actually, there is one way UIKit might make its way over to Mac and replace AppKit. Apple learned a lot of lessons over the years on what kinds of things a GUI framework should and should not do. We've also come a long way in terms of computer optimizations. AppKit has plenty of obsolete "sore spots" (like NSTableView) which make it a pain in the ass to accomplish goals that are very straightforward in UIKit. There's no reason Apple can't throw in a new "UIKit" as an alternative to AppKit, on the Mac. That way, developers could opt-in to using the newer kit, and life would be a little easier on us. Plus, this would also allow Apple to invent new paradigms and controls that don't quite fit on a touch-based screen, and which we've never thought of doing before on a mouse/keyboard-based screen. (Apple's good at this sort of thing.) I don't see this as being unlikely, but I'll bet they aren't going to do it for a few more years still.
Either way, whatever happens with WWDC, I'm certain the Mac is still going to stick around. It makes Apple a lot of money.