@Jake: The Canonical tag should be more like a last resort than an approach to fix dublicate content issues. The thing about relying on the Canonical tag is that you might not get the benefit of incomming links to the dublicate pages.
So you should avoid public dublicate URLs in the first place.
@RobShaver: Good approach eliminating the ".nsf" in the URLs, but why not take the full step? You got URL folders like /a/ or /nav/ in your web page URLs. As with the ".nsf" extension, it would be a lot better not to bother users with that kind of noice.
Substitution documents can take care of that problem quite nicely, as seen here: www.e-conomic.com