While researching how to add the +1 button, I came across this interesting tidbits on using rel=canonical to consolidate +1’s to the canonical version of a page. This bit from the FAQ is interesting because it mirrors advice on canonicalizing URLs to consolidate link juice, which points to a possible future in which +1’s enjoy a similar level of algorithmic importance as links do. Otherwise, why bother to worry about canonicalizing for them, hmmm?
From Google’s +1 FAQ:
However, your site may make the same content available via different URLs. For example, your site may have several pages listing the same set of products. One page might display products sorted in alphabetical order, while other pages display the same products listed by price or by rating. For example:
If Google knows that these pages have the same content, we may index only one version for our search results. As a result, +1’s for the other versions may not appear in search results.
You can make sure Google displays +1 annotations for the most search results possible by adding the rel=”canonical” property to the non-preferred versions of each page. This property should point to the canonical version, like this:
This tells Google: “Of all these pages with identical content, this page is the most useful. Please prioritize it in search results.” Now, when a user +1’s a page with a non-canonical URL, Google will associate that +1 with the canonical, preferred version.
Originally posted on Web PieRat.