While Mac users will have to wait for Yosemite before they can take advantage of iCloud Drive on Mac, Windows PC users get a treat today with iCloud Drive support through an updated version of iCloud for Windows. The update enables a folder within Windows Explorer (under Favorites) that allows iCloud users to view and edit files, drag & drop, and create new folders. Of course you'll need to be running iOS 8 to take advantage of iCloud Drive at all.
To grab the iCloud Drive update for Windows, head to Apple's support page here.
Source: Ars Technica