I am actually at the point of wanting to reinstall my Mac as well as my Windows VM when I find the time (this is a work machine that I use daily) because  do have delays.  
What is the history of your machine?  Mine started out as Leopard (I think), then Snow Leopard (or maybe it came with SL -- I really don't remember), Lion and finally Mountain Lion.  I think I started out with Parallels 4 or 5 then upgrade with each minor and major release.  I wonder if something in one of those various major upgrades has something to do with it.  I think my Win7-x64 VM also started out with the initial release and now is running the latest service pack.
Its also gone from running Symantec Anti-Virus (corporate) to Sophos (corporate), back to Norton Antivirus (home) and now back to Sophos (corporate) while my Windows VM went from Symantec (corporate) to Sophos (corporate).
					 
				
			
			
			
		 
		
		
		
			
			
				Last edited: Oct 19, 2012