"Access virtual machines hosted on VMware vSphere, ESXi or Workstation"
This makes it an essential upgrade even if it was the only new feature! And as a professional product, most people will have been upgrading each year anyway.
It also looks like version 6 isn't supported on Yosemite...
I'm running Fusion 6 and yosemite with win 7 and KALI Linux and it runs like a champ!
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Will Fusion 6 still run on Yosemite ?
Yes. Runs great on my '14 rMBP!