Pinax is a project created by the Django Hot Club, a group of developers aiming to produce quality reusable pluggable applications for Django. Pinax itself is an application that leverages a number of these modules, providing social media staples such as friends, interest groups (with associated wikis and forums), shared bookmarks (that can be rated, Reddit-style), etc. I haven't yet looked at the code, but the interface looks clean and I get the impression that this project could become the killer app needed to take Django's user base to the next level.
Drupy is an ambitious project aiming to port Drupal from PHP to Python. They seem very methodical in their approach, even creating a Python module that supplies ports of many PHP standard library functions. They are aiming to port the latest version of Drupal and it wouldn't be inconceivable that when Drupal 7 is released they could have their Python version ready. Very exciting.