Interesting question, it is said that Zope programming (Zope2, that is), is the least "pythonic" of all the python development framework, there is a lot of "black magic" happening in zope, for example, you need to be aware that your "application" (called Products in Zope2) will use the entire Zope machinery such as Authentication, Acquisition, authorization and so forth, as a developer, you "have to" rely on them much the way as developing in the microsoft .Net platform for example, you have to drink the kool aid no questions asked.
Though the functionality of zForum is very similar to pyForum, they are two very different beasts, I'd say that about 15% of the code in pyForum was borrowed from zForum, take a look for example to the authentication/authorization mechanism in pyForum, I ended up rolling my own, which is surprisingly similar to web2py's own, and I can honestly say that nothing was "borrowed" from web2py, I poked inside web2py innards just to see in what way authentication and authorization was being handled, and made a very small, but effective module that makes pyForum its own "unit" (I have the source code posted in my blog at
http://www.julioflores.com/zblog/blog/view/15). In Zope, I had to rely on external add-ons for authentication (which made the product depend on MySQL as the only RDBMS supported), and another external add-on to handle form authentication, and so on, yes you can "code" all the stuff yourself, but that means spending extra 3 months coding these parts.
Now don't get me wrong, I respect Zope a lot, in fact, I think ZPT
(http://en.wikipedia.org/wiki/ZPT#Zope_Page_Templates) is in many ways superior to all the mark-ups around, but I am really sad that Zope has taken a very different approach with a brand new, extremely hard to adopt paradigm that literally made me start looking around for something new (and guess what I found

).. I coded in Zope (along with python for other projects) hands on for 10 years, web2py was a welcoming breath of fresh air.
Coding in web2py was (still is)
fun, I enjoyed developing it, because almost everything is pure python,
I guess that it all comes down to that, during the development cycle of pyForum (that took about 3-4 weeks) I had one Browser opened up on zForum (the UI, not the code itself), and in another "workspace" I had all the pyForum stuff, I basically developed it that way, checking out the functionality of the former and applying it to the latter while at the same time optimizing it or changing old paradigms, etc.
Sorry for the long post, hope you're still awake

I just thought it was a good post to describe the "similarities" between both products, thank for bringing it up Richard.
Regards,
Julio