Depending on what you're prototyping, it could very well be done faster with Django. Django provides a bunch of 'generic views' which can make tossing up lists of objects from the db very fast to get started with. Then usually you end up fully replacing it all later, but it gives you a good start.

My views haven't changed since I answered this: http://stackoverflow.com/questions/48681/pros-cons-of-django...

If your app doesn't clearly fit into the sweet-spot's for Django, the argument will be less compelling. The pyramid code-base does have a lot of maturity behind it, it's not completely brand-new, so I don't think it'd be a problem to develop against it to be able to utilize its additional extension points.