As cool as a Rosetta for Windows would be, I think that the best it'll probably ever get will be like with Parallel's Coherency. I'd imagine that there are just too many Windows apps that do things in a wonky manner for anyone to get Wine/Codeweavers to work with virtually everything like VMWare/Parallels does...
Well, if you recall, Classic worked in much the same way that Codeweavers does. It wasn't 100% compatible, especially with software that tried to access hardware in peculiar ways. I can't count the number of applications that were rock-solid in OS 9, but were either unstable or simply wouldn't run at all under Classic in OS X. Essentially, I gave all these applications up. Would I want to go back? Absolutely not.
So, if Apple introduced an equivalent to Classic for Windows apps (which, one could easily argue, is closer to what Parallels is doing with Coherency, but see my comments farther on about where I see Coherency falling short of the mark), based on the WINE, even if it couldn't run a lot of Windows programs, the ability to say "Now Mac OS X can run most common Windows applications through our new WINE-X emulation layer..." would be incredibly powerful. Would it run everything? No, but neither did Classic. Would it gain more switchers? Most likely...
...Boot Camp is cool, however I think most average switchers are going to be looking for the non-obtrusiveness that virtualization gives them, and I think Apple could do a better job in helping deliver that. No?...
My personal pet peeve with virtualization, dual boots, etc. is that they aren't unobtrusive. Why? Because you end up storing your files in multiple different places. You loose double-click functionality. And so on.
Suppose you have your system set up to work with the "unobtrusive" method of Parallels Coherence. Someone emails you a Word file. Because you have this unobtrusive set-up, you only have Office for Windows. Can you double click on the file? No. Can you save it in your documents folder and then open Word to open the file? No, because Word sees a different file system, a different disk, etc. (Sure, you can share your whole Documents folder with your VM, but then what if you dragged the file to the desktop? Do you just set-up every directory on the Mac side as a share with the VM?) And what if you write a document in Word, then save it and later want to attach it to an email? Well, if you saved it on the VM disk, you'll have to drag it out of there, right?
Let me go ahead and say that I haven't tried Parallels or VMware, so I don't know how seamlessly they have managed to implement file sharing between the host and guest machines. To a significant extent, I'm speaking from experience with VPC, and a couple of other emulators from years gone by.
What I really want is a means of running applications where OS X can handle file recognition, so I can double click; an application icon appears in the Dock; and the application runs in the same filesystem as the main system. Codeweavers CrossOver gets a lot closer to this than either VMware or Parallels, from what I've seen, though Parallels Coherence is a step in the right direction. I don't have an issue, so much, with running a full instance of Windows. If only a means could be determined to run it in the same way that a full instance of OS 9 was run inside of OS X to give us Classic.