Plugin architecture

[mk]

Hello everyone,

I'm thinking about writing plugin-style architecture for (a new) 
web-based app (with SQLAlchemy as backend).

Say, there's core web app and someone decides to write plugin Accounting 
for this web app that would work with SQA objects of the core app or 
other plugins.

I found this:

http://effbot.org/zone/metaclass-plugins.htm

(Although I'm not entirely sure this is the best approach for the web app)

How would you approach designing such architecture using features 
available in Python (and some major web framework, like Pylons or Django)?

Regards,
mk