For those still living in Plone 4 land, just a note about something I've come upon.
As of Plone 4.3.4 some older archetypes based products break with an error like this:
AttributeError: type object 'ATFolder' has no attribute '__implements__'
I figure I'll need to fix something with my old products before I can proceed with an upgrade. If you've come across this and know the solution feel free to share. I plan to troubleshoot at some point. For now I'm pinning sites that depend on this product to Plone 4.3.3.
It looks like your product tries to explicitly extend an old-style __implements__ declaration which is no longer present in Archetypes. You'll need to switch to new-style interfaces (from zope.interface instead of Interface, and using implements or @implementer instead of __implements__)