In a blatant act of self promotion, now that pownce is finished, I can confidently write that we are the only other django based micro-blogging network with some traction. I do admit the user interface needs a bit of work, but if you interact with our community, you will realize that they are a set of amazing people.
So keeping in mind that you want to move on from pownce, try something new … or just try kwippy.