It is a short post-though about two popular Python frameworks. This is my personal experience and some analytics.
Well, if you building long-term project, for example some social network (oh again), usually you need rapid prototyping and then step-by-step (iteration) development. For prototyping you need more and more components, which you can replace or customize later. For iteration-based development you need to setup release deployment and testing automation (aka buildbot). Important thing that you have deployments on own infrastructure and you can build it once and then forget. So Django is number one solution for the component-based model (aka apps).
Other case is when you creating an application which would be highly redistributable, for example blog or e-shop engine. It is really hard (for today) to setup quickly django applications and lots of people is aware of hand-made installations (like terminal commands, etc). Pylons has a better deployment tool (paste) that helps with redistribution of projects and better project/app file layout.
It is main reason why there are still not so much complete django applications.
I thinking to use both for different cases, but anyway large projects is a Django way.