I finally decided I had to downgrade to 3 (and did so this morning). The lack of true full screen support (come on guys, it's not hard) in Lion is a minor annoyance, but the real kicker for me is the completely broken implementation of shared folders (see http://communities.vmware.com/thread/332152 and the linked thread it contains).
I'm always an early adopter, but this time the I/O erros made me regret it.
I also downgraded (because of a different problem described in full in another post).
The downgrade worked well, in fact it's just a full 3.0.x reinstall, and because of the "old versions cleanup" step at the beginning of the Fusion 4 launch, you cannot keep both versions installed. Or maybe you could with a hidden pref I'm not aware of?
I had problems with 3 and 4, so I tried and purchased parallels, NO MORE PROBLEMS!!!!!!!
Ever since I upgraded to 10.7, fusion was a nightmare for me, it destroyed my boot camp just for starters and other very very annoying problems!!
Oh one more thing parallels is very quick!
Best of luck