g1smd - 2:17 pm on Mar 15, 2010 (gmt 0)
But do register both
www.example.com as separate items in Google WebmasterTools and look at both reports, especially the 'crawl errors' and the 'internal links' and the 'sites that link to you' reports.
Try to find incoming external links pointing at the non-canonical version and over time work on getting those other sites to adjust their link.
Additionally, for any sites where their link to you includes an index page filename such as index.html or index.php or default.asp get them to remove that filename from their link, ending the URL with just the trailing slash. That is their link to
www.example.com/folder/index.php becomes a link to
www.example.com/folder/ and so on.