Well, actually isn't it the same as if you redirect your URLs to the preferred ones - either with the www prefix or not and index.html/index.php to the domain. Actually haven't you all done this yet, before the attribute was announced? Otherwise thanks for the news
It is an easier way for the /index thing, but I don't think it substitutes with a 301 Redirect for the www
Does this one <link rel="canonical" ....> also needed for .blogspot.com owners? For web master they understand "duplicate content",but how about the bloggers? With no such knowledge about this? Maybe this question should be answered: "Does this tip apply to blogs? If so, how would one want to implement it?"