Django vs. Grok / Zope3 vs. Pylons

I am a computer programmer by training but have been away from web development for a while. I am doing a little bit of background research on various Python web development frameworks. I understand that Django, Grok / Zope 3, and Pylons are all good solid frameworks, but have little in the way of background working with them. Can someone explain to me the difference in approach of the each of the frameworks, and where one shines when compared to the others?

My specific use case is in building a web application that will recommend products to users based on a variety of user supplied information. Thus, it will take a fair bit of user input in the shape of a basic profile, product preferences, attempt to establish social relationships between users. It will also need to support staff uploading products into the system with labeled features that can be then matched to users.

On the last point, would parts of Plone help with providing an interface for non-tech people to upload products and descriptions of the products? Are piece of Plone easy to borrow? Seems like I shouldn't have to reinvent the wheel in terms of having a way for people to upload items for sale / recommendation along with some metadata to describe the items. Thanks for the help.