When I run VMWare Fusion in Unity mode, is there any way to see the desktop or access the files on the desktop? Or must I switch into Single Window/Full Screen mode?
You cannot view the windows desktop as the "Desktop" in Unity (As @mankoff said, you can open it as a folder). The intention of Unity is to Run Windows apps "side by side" with Mac apps. This means the Mac desktop is the desktop.
I remember there was an option to "Show taskbar in unity" in a older version. Unable to find it in version 3 (did not look for long, anyway I think this is not very useful)
BTW, the way I use VMWare is only for application installs. All my data still stays on my mac (in a special folder if required) but not inside the VM. Helps me back them up, email them if required (even when the VM is suspended). So I never felt a need to see the desktop.
You can view the Desktop as a folder in Windows Explorer.