Disk security methods already in place will be removed on installation, unless Windows 8 plainly refuses to use the disk because it can't partition it. We applaud Microsoft's attempts at boot security, and don't have the qualms that others find when a vendor tries to secure a system. Yes, it makes it a hassle to have other operating systems on the same system -- that's what virtual machines and workarounds are for. The security trade-off, we feel is worth it and is only small discomfort for hackers -- who have already suggested clever workarounds.
We ran into one case where a pre-release version of Windows 8 wouldn't install without removing older partitions, but all upgrades we tried from Windows 7 to Windows 8 worked flawlessly and without complaint or annoyance. Microsoft suggests that anywhere Windows 7 works, Windows 8 should install; the only limitations we've heard anecdotally are where drivers for advanced displays just aren't available yet; we didn't run into this problem in 11 installations.
The Windows 2012 Key Management Service allows instances of W8E to be installed, grabbing an activation key when initially installed. This works with Windows 7, too. The operating system payloads can also be modified to deploy both Microsoft and third-party software for automated updates, although Microsoft's System Center 2012: Configuration Manager handles this chore with better finesse than manual payload management.
Windows 8 opens with the Windows 8 UI (formerly known as Metro), which is also found on Windows Server 2012, Windows RT and Windows Mobile 7.5+. This cross-platform UI ideal has also been championed by Apple with iOS (even MacOS devices are starting to look like iOS), Canonical with Unity on Ubuntu (desktop, server, tablet, and beta smartphones), and is desirable as the proliferation of personal device learning curves and seeming inter-device family incompatibilities arise.
The UI isn't tough to maneuver at all, we found. A fast mouse-movement to the right of the main UI reveals options to change settings, and otherwise move around. Behavior of applications already installed shouldn't change. But there's a rub.