Hi ErocMillsie,
I've got a MBP 2009 running Fusion 4.1 (used it for 5.0 during the beta too) and this MBP 2012 runs Fusion 5.0.1
I can say that I'm quite happy with Fusion 5, it is very stable for me, haven't seen any new issues.
Actually I am happier with Fusion 5 as with Mountain Lion (big OSX Leopard fan here).
You have to remember that by closely following the forums you'll see the horror stories about upgrades not working well for people, they rarely post here saying how well it works. Just get yourself a good backup of your important VM's before trying it out, which I think is more for "feeling good about an easy fall back" as it being critical. Even after going to Fusion 5 and changing the hardware to Fusion 5 only you can still move that VM back to Fusion 4 if it doesn't work out for you.
Hope this helps,
--
Wil