I have just been reading about google canonical instruction, ive never used it just wondered if anyone is using it and what kind of sites should be using it ?
As apart from it being really hard to say, its very hard to follow lol
It is for telling google you have duplicate content pages. In the link you gave, it says the following, which is an explanation I dont think I can do better:
"Now, you can simply add this <link> tag to specify your preferred version:
