How do you manage your Django applications?
Just like any set of dependencies... try to find the most useful stand-alone aspects of the project and make those stand-alone apps.  Other Django Apps will have higher level functionality, and reuse the parts of the lowest level apps that you have set up.
In my project,  I have a calendar app with its own Event object in its models.  I also have a carpool database set up, and for the departure time and the duration I use the calendar's Event object right in my RideShare tables. The carpooling database is calendar-aware, and gets all the nice .ics export and calendar views from the calendar app for 'free.'
There are some tricks to getting the Apps reusable, like naming the templates directory: project/app2/templates/app2/index.html.  This lets you refer to app2/index.html from any other app, and get the right template.  I picked that one up looking at the built-in reusable apps in Django itself.  Pinax is a bit of a monster size-wise but it also demonstrates a nice reusable App structure.
If in doubt, forget about reusable apps for now.  Put all your messages and polls in one app and get through one rev.  You'll discover during the process what steps feel unnecessary, and could be broken out as something stand-alone in the future.
I just wanted to try to build a project with django. Therefore I have a (basic) question on how to manage such a project. Since I cannot find any guidelines or so on how to split a project into applications.
Let's take a kind of SO as an example. Which applications would you use?
I'd say there should be the applications "users" and "questions". But what if there was a topic system with static articles, too. Maybe they also could receive votes.
How to build the apps structure then? One app for "questions", "votes" and "topics" or just one app "content"?
I have no idea what to do. Maybe it's because I know not very much about Django yet, but I'm interested either...