I've just implemented the _trackPageview() functionality exactly as described in http://contactform7.com/tracking-form-submissions-with-google-analytics/
If this is enabled, then no Ajax success message is displayed on successful form submit. The form does submit and the message is sent, but the user doesn't get an indication of successful submission.
If I delete
from the Additional Settings section, then the success message displays correctly.
You can see this behaviour at http://bit.ly/KnUmOh