What about volume and site licensing? The App Store approach is great for home users, but I can't see it playing out well in schools or businesses where a base configuration and set of apps needs to be made available to a large number of computers. This is already a challenge when deploying iPhones and iPads in bulk, and has been since the App Store launched over two years ago. While iOS 4 addressed many enterprise concerns, it left a gaping hole in terms of mass deployment of apps. Apple could resolve this challenge by including an app management and license server feature in Lion Server.
Auto-save and auto-resume
I like the concept of Apple building the ability to auto-save files into Lion so that every developer can easily include it in their applications -- so long as it doesn't lead to file system challenges like those on iOS devices (where there is no central access to a file system) and it doesn't mean that traditional Open and Save dialogs and methods are going away (which I doubt). Let's face it; we've all lost work because we forgot to hit Save often enough, so this is a big plus.
It would be nice to see this feature tied into some form of revision history. I'm thinking particularly about the ability of Google Docs and Dropbox to find previous versions of a file if you decide you don't want to keep the changes that you (or someone else) made to it. Given that this feature exists in a somewhat limited form with Apple's Time Machine, I don't see it being a big challenge to create, and it is a natural extension of the auto-save concept.
Auto-resume is something I'm less enthusiastic about. It works well for mobile devices that display only one application at a time because you have to switch in and out of apps frequently. I'm not sure I want or need that in my desktop apps. Most of the time when I launch Word, for example, I want to start a new document rather than automatically seeing the last document I had open; otherwise I'd have double-clicked the document I wanted. So I'm hoping this will be an optional feature that users can enable or disable as whole or, better yet, on an app-specific basis.
Launchpad and app home screens
I wish I was excited by the demo of Launchpad, a feature that displays all installed applications as an overlay on the desktop similar to the iOS home screen, but I wasn't. The idea is to have all applications (presumably from the Mac App Store as well as other sources) available with one click -- and perhaps some swiping to see more app screens if they can't all fit onscreen at once. (You can get a similar effect by dragging your Mac's Applications folder into the Dock as I've done on each of my Macs.)
The concept isn't a bad one, but it's too easy to go from a good idea to a bad experience with it.
Any longtime Mac user might remember that Apple has tried this concept a few times over the years, first in managed workgroup and multi-user products such as At Ease and Mac Manager, and as an option in classic MacOS releases. In some cases, the MacOS Finder was completely replaced by a button-style view of installed or allowed applications. In others, a button view was introduced as an alternative. Perhaps the most commonly known and best-designed implementation was the Launcher. It should be telling that none of these solutions exists today.
Launchpad does seem an improvement over past attempts at streamlining and access restriction. (I imagine Apple will integrate it with parental controls and client management via Mac OS X Server and/or third-party Active Directory solutions.) But it could be just as confusing to some users as having to locate applications in the Applications folder and its subfolders.
I'm particularly put off by the idea of iOS-style folders in Launchpad. This seems to increase the potential for confusion and onscreen clutter, particularly if more traditional ways of launching applications remain: drilling down through folders, opening a specific document, keeping applications in the Dock and using Stacks in the Dock to browse through your Applications folder or other folders -- not to mention applications stored on removable media such as external hard drives, DVDs and network shares. Adding to all of those options, Launchpad with its various screens of apps and iOS-style folders seems to make application management more complex by the sheer number of choices rather than simplifying the process.
On the other hand, it also allows individual users to work in whatever environment they feel most comfortable. I think the key here is going to be how Apple ultimately delivers Launchpad as part of the OS. It should still be clear, at least to power users, where the applications are stored in the file system. Apple needs to give users complete preference in how they work with applications, regardless of whether they're installed from the Mac App Store, downloaded from another source, bundled with Lion or, in the case of users who upgrade to Lion, already exist on the computer from a prior version of OS X.
When I first saw the combination of features (Exposé, Dashboard, Spaces and full-screen apps) that Apple pulled together to create Mission Control, I was afraid that it could work out very badly. Having had a glimpse at the result, I think Apple did a pretty good, though not perfect, job.
I absolutely love the idea of swiping to move between screens (or Spaces); it's an effective solution for both full-screen apps and traditional windowed applications. I like that Exposé is incorporated, letting you see previews of individual windows and Spaces and switch among them quickly. I can see this combination working brilliantly.
I also like that it's a completely natural carry-over from iOS. Unlike with Launchpad, I think Apple nailed this marriage of features from Mac OS X and iOS, making a really useful new form of navigation.
The one thing that I don't get is making Dashboard a separate screen instead of having it appear on top of the current screen. To me, one of the big advantages of Dashboard is that I don't have to leave what I'm doing to check the weather, verify someone's phone number, control iTunes, make short notes to myself or do some quick adding/subtracting using the calculator. (And that's just a few of the built-in widgets; there are plenty of useful third-party ones as well.) I hope the fact that it was displayed in its own screen was just part of the demo -- or that Apple will change it back to its traditional mode before next summer.
The bottom line on Lion
Longtime Mac users (and even some new Mac users or Windows users thinking about making the switch) may be wary of some of the interface changes in Lion. A hesitation about them at this point is a perfectly valid. Apple clearly has some great ideas, but it will come down to how they're implemented to determine if they'll be reasons to celebrate or vilify Mac OS X Lion. And that's something we won't be able to judge for a while yet.