Django 1.5 is making it impossible to test, as far as I can tell; you get a circular dependency error that I wasn't able to work around. It's not the best strategy anyway; it's best to put logging in a separate database, perhaps even on different storage or a different server. You'll regret a single database when something goes haywire and you want to clean up the resultant logging and reclaim the space, without affecting the rest of the site.
Usernames can change, of course, so recording the primary key as well ensures you can positively identify the user being logged. The schema is migrated to add the user PK, but I've not included a data migration to automatically update it on existing log records.
By default, peavy should be doing its database logging on a different connection than the application uses, so its commits don't interfere with the application. Added unit tests. Well, test, singular, to verify that the logging is persistent even if the app transaction is rolled back, and that logging doesn't commit app writes, thus preventing them from being rolled back. Added a demo app to show how to configure and use it, and to show the UI. Maybe it'll light a fire under me to improve the UI.