Microsoft has long had a slew of tools to simplify the job of migrating users and desktops to a new version of Windows. The exact tool set has changed over time, but at its core are tools for two kinds of jobs: upgrading an existing machine to a new OS, and moving a user's settings to a new machine with the new OS. Microsoft calls these "PC refresh" and "PC replacement" scenarios, respectively.
The refresh vs. replacement scenario may be a little more crucial with Windows 8 than with previous versions of Windows. For instance, there might be tentative plans to migrate an existing fleet of notebooks to touch-enabled devices to make that much more use of Windows 8's touch features.
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This isn't to say that an existing non-touch PC won't work well with Windows 8. It's more that the most compelling use cases for Windows 8 involve touch-based hardware, most of which might well be a new addition to the hardware fleet in your organization.
A major component in upgrading to Windows 8 will most likely be the User State Migration Tool (USMT), provided as part of the Microsoft Deployment Toolkit 2012. USMT allows a user's state -- account information, local files, and application and OS settings -- to be captured and stored as a file, then migrated to an entirely new installation of Windows. The newest edition of this Windows migration tool, Version 5, adds in support for Windows 8 migrations, so you must use this version if you want to start staging user migrations to Windows 8; earlier versions won't work.
For moving user data between individual, unmanaged PCs, there's the Windows Easy Transfer utility, which was introduced back in Vista. It's used to create an archive of the user's files and application settings, which can either be transferred directly over a network to the target PC or saved to a file and then re-opened there. Note that when migrating to Windows 8, you need to use the version of the tool supplied with Windows 8 itself (in the \support\migwiz folder of the installation media), rather than a version supplied with previous editions of Windows.