In the recent interview of Adam Lasnik by Eric Enge, it was noted that Google has become pretty efficient at determining the intended versions of web pages. By submitting a .xml sitemap to Google with your intended version of the site, you can minimize the chance that Google will get this wrong.
“There is one other tip here though that can also help Webmasters that have this particular problem. That is to submit an XML sitemap using our webmaster tools, because what we’ve been doing increasingly is taking a look at the URLs that are submitted on that sitemap, and using that as a canonicalization hint. So, if we are uncertain whether we should be using the, just site.com, or site.com/index.html, but, you list site.com and not site.com/index.html in your sitemap; we are going to be more apt to go with that.”
More surprising is how Google attributes all link juice to the proper version of the page, even if sites link to other versions internally or externally.
“When we canonicalize stuff on our end, we also combine PageRank. So, if we see that people are linking to the exact same resource in three different ways, again thankfully in the majority of cases that I have seen, we are able to not only know that’s the same page, we are also able to take the different links, the different URLs that are linking there, and combine that PageRank so that it gets the total PageRank from those links, and it’s not separated out.”