Forum OpenACS Q&A: Response to Article on ACS x Zope
It is efficient in the way that it uses the file system or the database according to what's best. Static pages, for example, are kept in the file system, and are stuffed in the DB just so they can make use of dynamically generated things and for searching (which is not working under PG yet).
I'd say that the ACS is very nice. The main drawback was the lack of true modularity, but that will be done with ACS 4 which should be out in June if I am not mistaken. It will be even more butt-kicking than it is.
I haven't done anything with Zope, but I read a bit of the documentation and I have to admit that I was overwhelmed. I think both systems can learn from each other as you said and I hope that happens.