On FUDCon Brno 2008, we gave a small overview on how to use PolicyKit to split an application in a two parts with different privileges.
Now, here comes the practical part. Nils Philippsen wrote a small python module, which greatly simplifies the use of PolicyKit for python applications. Downloads, git repo and more information, along with simple example code can be found on http://fedorahosted.org/python-slip/
In its current form it uses D-BUS communication to check policykit action_ids, which will change, as soon as the python bindings for PolicyKit will be released (hint, hint!).