I have not discovered any plug-ins that don't seems to work in 10.7, or Logic Pro 9.
The real issues are between the 64 VS 32 bit changeover. The fact the 32 bit plug-ins are only accessed by the bridge app, a pretty crappy solution at best, is where i find almost all my issues show up.
I've been working exclusively with 64 bit plugins for the past few months so that won't be an issue for me. Someone here in Montreal had said that he felt like his 8 core MacPro was running more slowly on Lion. ???
On another note, Eli had told me that you're using a MacMini? Do you have any noise issues with it? I'm interested in the MacMini server / 2 x 750 GB HD / OWC 16 GB Ram kit. I'd like to use it as a Vienna Ensemble Pro host machine.