There are apps currently compatible with Windows 7, and those should run OK. Apps that use the new Windows 8 UI are called Windows 8 apps, and can be obtained (ostensibly) only from the Microsoft Store. The store is currently starting to fill, but by no means has the quantity found in Apple, Google or Amazon app stores. The regimen used to vet applications in the store is also still largely unknown.
Other items we tested include: the Windows 8 User State Migration Tool, which allows user settings to be migrated to a new machine (similar to the older, Windows 7 version); Windows To Go, which makes a bootable (think USB Flash Drive or other externally connected drive) instance, system hardware-permitting; and we played with making customizable Windows 8 P/E images for distribution purposes.
By combining these tools, coupled to server-based key management tools, deploying Windows has been made almost as simple as an online Linux distro. It's still Windows, and uses a hallowed convention for file placement and licensing, but we found it easier than Windows 7 at image customizing.
The Windows 8 UI takes just a moment to understand; it's not quite an intelligence test. On our Lenovo T520 tablets -- on the same hardware -- Windows 8 boots in 16 seconds to usability in a fresh installation vs. Windows 7 (with updates) at 27 seconds. We could detect no real disk speed changes, but the UI is fast and has a "snappy" feel when we changed screens, or popped back to the Windows 8 UI with the Windows key on the Lenovos.
We were mystified that sleep, hibernate, and other control options were absent from the Windows 8 UI choices. These worked, but we like to choose them ourselves sometimes, rather than close the lid on our notebooks, or shutdown via hibernate switches on our desktop machine, but these are small grievances.
This is the first Microsoft client OS that hasn't been directly compared with Apple's MacOS in ages. With Windows 8, Microsoft deviates from the course of evolving their UI into stratifying their UI across the platform segments that it supports.
Windows 8 isn't quite as radical as Windows Server 2012, but the unified UI strategy is a departure from UI and iterative functionality improvements. Windows 8 is more distributable, more easily secured, and works hard to retain an enterprise presence. Old software works, new software installed without issue if it works with Windows 7. What's for sale here is cross-device unified behavior atop the gains made by Windows 7.
We still fear a dot-zero release, but with as much advance pounding as this release has seen -- it was in general beta for a year prior to our ability to obtain RTM code -- it seems (dare we say it?) safer.
Windows Server 2012 (Standard and Data Center)