I have the same problem -- but find that if I hard boot the Mac (hold down the power key), typically I will get a Can't load/recover message about workspace (or something like that) from Fusion and if I select Discard, then the image loads fine and the old performance is restored.
I do NOT like to have to do this type of hard reboot (one of these days, it will go to purgatorio!), but it does suggests where the problem is -- fragmentation of this.
I'm running 7.1.1 VMware Fusion with Windows Server 2008 R2 x64 OS.
I do not see an option for app nap when I do a get Info.
