GeoDjango: getting a random point within a multipolygon

While fooling around with the awesome GeoDjango framework, I was looking for a way to generate a random point within a multipolygon.
Justin Bronn (djangopeople.net/jbronn/), the lead developer of GeoDjango was kind enough to point me in the right direction. I thought I share the concept here as it might be helpful to someone:
Define the function:

def [...]