In my personal experience (7D) the auto clean did sh*t...
I got spots everywhere, but that was also because of continuos lens changing in bad environment (cycling events), so i can't blame it.
Though I found that using whenever I remember my trusty rocket blower helped incredibly!
I usually blow some air whenever I change the lens, or in case i forget, whenever I remember.
From that moment onwards I got almost little to zero dust spots