Well, I've been experimenting with the Windows (8) Developer Preview in more depth, and I'd like to share my thoughts and experiences.
Program compatibillity is of course one of the most important factors in deciding whether to switch to a new OS. I was also curious to see how the Metro interface would handle newly installed programs. So I downloaded and installed current versions of Firefox (9), HandBrake, and Spybot Search & Destroy (1.6.2). These three programs have worked flawlessly so far.
If the program goes through an installation process, a new plain tile with the program's name will appear at the far end of the Metro start screen. If you expect to use the program often, you can drag the tile over to the left end, although that process is somewhat clunky.
One interesting (not sure if good) outcome is that the individual subprograms within a main program get their own tiles. For instance, after installing Spybot I ended up with tiles for main Spybot, the file shredder, the update function, and uninstall. I wonder if it's possible to merge these back into one tile -- install enough applications, and you could end up with hundreds of tiles and tons of Start screen pages to scroll through. The current, "classic" All Programs menu makes for a much more compact lookup experience.
One note about Spybot 1.6.2: Remarkably, this little program works without modification or glitch not only on Windows 8, but all the way back to Windows 98 (and 95, for all I know).
The same thing, unfortunately, can't be said for the Spybot 2 beta, which I tried using before 1.6.2. It didn't work: I kept getting errors about a missing this and an invalid that, culminating in one of the newfangled BSODs with the "sad" emoticon. I suppose that it was a bit optimistic to run beta software in a pre-beta OS and expect everything to work.
The crash leads me to an observation about the new BSOD: It automatically reboots the system after a few seconds -- plainly not enough time to take down the error information (which additionally is given in small, low-contrast type, which means that it takes even longer to discern what it says). This is not a step forward. Feature improvement: Do NOT reboot automatically, give the user the chance to pause the process so he/she can write down the error information! If this is already possible, then for heaven's sake tell the user how to do it (in easy-to-ready type) ON THE BSOD SCREEN.
I just returned to the Windows 8 preview after letting it work overnight. Went back into the Start Screen, and lo and behold! the weather app has once again returned to showing me the weather in what it sems to consider the center of the universe -- Anaheim, California. I've already changed it to a town in my own state TWICE, and (thought I had) removed Anaheim from the display options. What's up with that?
Update: Next time I returned from typing this to the Metro screen (it's on a different PC), the local weather info had returned on its own. That's good, but I thought that a selling point for these Metro tiles was that they provide information the user wants, so why not just give the local weather that the user has selected, in the first place?
More about app tiles: You can't right-click on an app in the Metro Start Screen to reach the context menu in order to look up properties, rename it, scan it with security software, or run it in administrator mode. For that you have to go to the Desktop... and be lucky or prescient enough to have a program icon for it, since you can't get into the REAL Start Menu. Right-clicking on a tile (or on the search result, if you used the Metro Search function) simply places a check mark of mysterious significance in the upper right.
One last thing: I haven't found a way to select Safe Mode if you want to boot into it for a given reason.
EDIT 2/26/13: Added subtitle