This is essentially a complete revamp of the OS. Depending on how the drives are seen by the bios and the board you are using, if you are using a dual boot system, the upgrade will fail with 0x80073BC3-0x20009 error and will reverse the install back to 8.0. You are advised to disconnect you Mac OS drive and and complete the upgrade install independently, no other drives in the mix. Reconnecting back will work fine with Chimera bootloader. (If you don't see percentages of completion after reboot during the upgrade process, it has failed to upgrade and will reverse back to 8.0)
Further, if you are using Microsoft Tookit to activate Office 2013 if will be deactivated and you will not be able to reactivate at this time. Office 2010 does not have the same issues.
There will be a WindowsOld folder created, after the upgrade, (Hence the complete revamp), and this can be deleted using Disk Cleanup through administrative tools selecting cleanup system files, and then choosing remove old windows files, but beware, this is not a reversible process.
Forgot IE 11. Java incompatible, Acrobat plugins incompatible, and I am sure there other plugins that are incompatible with new security. Worthless upgrade. Microsoft not even addressing the fact that there are issues, blaming Oracle for the problem as far as Java is concerned.
This problem occurred in the preview and is still present in pubic release:
http://social.technet.microsoft.com...ken-in-windows-81s-desktop-internet-explorer-