[Zope] Scalability of Zope

Hi, I'm a Zope newbie. I've done some searches in the archives on 'scalability'. I'm currently evaluating Zope for possible use in a high traffic situation. I have seen discussion on the multithreadedness of ZODB3 (in Zope 2), which is good news. What other issues or concerns are there with Zope in regards to scalability? How have people been setting up Zope, and what's the largest Zope installation that you know of (in terms of machines, database size, and traffic)? I like what I see in Zope and hope it will be useful for my applications. Thanks for your help! Philip Suh