So this author would lead us to believe that having different versions of the same page on your server is an issue?  Meaning your site will rank worse becuase of it.  Doesnt Google just filter out the secodnary versions of the URLs?  Playing devils advocate here.

I'd say that's sound advice. Google's canonicalization got a somewhat fishy smack considering that Google is in the obfuscating-canonical-URIs-by-creating-many-cluttered-URIs-pointing-to-the-same-piece-of-content business now, because so many webmasters canonicalize their URIs properly and therefore Google's canonicalization routines idle ... ;-)

incrediblehelp -it's not an issue of Google filtering them out of serps - it's about different versions of the same page being linked to -

If you have different versions of the same page, then what happens is that more than one version gets links - people copy and paste the url of the page that they are on and post it in their blog, or bookmark it in del.icio.us or digg etc.

And then there's the same issue with internal linking, if your cms is automatically generating different versions of the url you'll probably find it's also linking in different places to different versions.

How can we set the 'Canonical' tag?

Put a LINK element in the HEAD section of pages suffering from cluttered URIs. RTFM