[Dec'2012 - Windows 8 has been added to the system requirements for Quicken 2013]
There is no version of Quicken that Intuit lists Windows 8 as a supported OS in the System Requirements.
With that said, users have written in saying that it works and others have had issues, but some of those I believe were issues with unfamiliarity with the new Windows and some permission issues. If at all possible, I would try testing your version on a Windows 8 installation prior to converting/upgrading the OS just to see what happens. YMMV
[added] This does not apply to Windows RT, it is definitely NOT compatible with it.