According to this article, "Apps would also have to go through a "service based delivery" system such as Windows Marketplace to install, reversing a years-old ability to download apps through the browser or other sources.". If that's true, I don't care how much of an improvement the interface is - I want no part of it.
Among other things, that would require you buy a data plan. As if PDA cellphone's couldn't possibly be useful without one. Sure, sure, you could just buy a dedicated PDA, but those are becoming increasingly difficult to find (certainly Palm doesn't make them anymore) and something does have to be said for device consolidation. I'd rather have a single HTC Touch Pro2 in my pocket than trying to stuff a cellphone, a PDA, a camera and a GPS unit into my pockets.
Further, even if you do have a data plan, requiring all apps be sold through the Windows Marketplace will give Microsoft an unreasonable amount of control. Remember Google Voice for the iPhone? Apple denied Google the right to offer it through their App Store because it competed with their own product lineup. What's to stop Microsoft from doing the same thing?
And what about apps that are no longer maintained? There's an SNES emulator available for Windows Mobile and a TI-89 emulator available for Windows Mobile. Both, near as I can tell, haven't been maintained since Windows Mobile 5 or so. If those apps didn't work in Windows Mobile 7 because the API changed, that's one thing, but it would be unfortunate if the only thing preventing those apps from being installed was the fact that Microsoft wanted more direct control. It's like being rejected for a job interview not because you're skills were insufficient but because you didn't put the right buzzwords on your resume to get past the regex HR was using to filter out resumes. Because you said PHP on your resume instead of PHP5.
But then again, it seems unlikely Microsoft would let anyone offer an SNES emulator or TI-89 emulator through their app store, even if they were to be actively maintaining it, on the basis that it encourages piracy or some such.