I'm wondering whether to upgrade to Fusion 5. I run a Win 7 64bit VM using Fusion 4 on a 2009 MBP running OS X 10.8. It does not run too badly, but improvements in the impact of the VM on the host system would always be welcome (i.e. lower cpu/battery usage, less spinning beachballs in OS X whilst the VM is running). If you have upgraded from Fusion 4 to Fusion 5 have you noticed much impact on these things?