3 is a pretty epic fail in my book.
The upgrade issues were the first big fail.
They removed or broke the headless functionality. Whereas in 2 I could launch my VM's at boot and have them available without having to login, I cannot do that in 3. It was also nice to be able to flip into and out of headless mode in the GUI, but that's gone as well.
That's the second big fail, and as I use my VM's for running Solaris x86 servers as well as Windows desktops, that was enough to push me into looking at VirtualBox.
Also, looking at the Fusion forums, there are a lot of folks having some significant issues with 3.
OTOH, VirtualBox seems to be running reasonably well. Performance is fine for my Window's VM, and I'm evaluating my Solaris x86 servers. I do seem to be running into a bug on the headless mode, but at least it's an officially supported feature and not likely to vanish at the whim of some company.
VirtualBox's interface isn't nearly as polished as Fusion or Parallels, but it works. Frankly, the interface looks is the last thing I'm worried about.
If you're looking at virtual machines, take a gander at VirtualBox, the pricing and upgrade pricing certainly are hard to match.
I won't say it's a total failure, but there can be some significant issues and one would be well advised to research thoroughly before upgrading.