Steve,
I have some very interesting new info on this issue in Fusion 5.
This morning, I performed a clean install of the newly released OSX 10.8.3 on my mac pro...and then installed the newly released Fusion 5.03 on it. I upgraded my Windows 7 & Windows 8 VM's by installing the tools, etc.
I immediately saw the shared folder freeze issue in my Windows 8 VM...however, this time, I was able to display Task Manager during a long freeze...and I saw the Antimalware Service Executable task using 30% of the CPU...as soon as the freeze ended...the CPU went to 0.
I then proceeded to disable the Real-time protection in Windows Defender on Windows 8...and now....the shared folder freeze issue appears to be gone.
This reminds me very much of a similar issue that I had with shared folders back in Fusion 3 with Avast! AV.
I am not seeing the issue at all in my Windows 7 VM…which only has the Spyware component of Windows Defender…not the Anti-virus component, as is standard in Windows 8.
I will continue to monitor this, of course…
Any thoughts?