[Zope] Social Networking over Zope

Hi all, I have recently been asked to build a social network site. My first thought was to implement it on Zope, but I'm a little bit worried about concurrency and scalability. Having such a site access continuously to the database, I guess its caching possibilities are very low. Anyway, what I really looking for is some advice. Anybody here to share his/her thoughts? Any past experience? Why is that most social networks are built over ASP.NET or PHP? Thanks in advance, a lot. Pablo PS: I still have to convince my client, so...