We knew that Google was trying to get their +1 button out to as many contact surfaces as possible. Starting with webmasters is just that – a start – so the release of +1 functionality on product searches and a built-in +1 button on product pages is hardly surprising. Here are some details on the release, however.
The functionality included is very similar to what you have on your SERP for normal pages; users can +1 the various products and their friends will see a promoted result indicating who shared it. Further, this is likely to be a ranking factor for the products themselves. To make this functionality possible, however, Google couldn’t rely on webmasters. Since Google Product Search combines all identical products into a single page and then gives options, price quotes, and rating for various sellers, there’s no “webmaster” to add a +1 button. So Google has done that for you. You can now find a +1 button on any product page.
All users will be able to see this +1 button, although you will have to be logged into your Google account to use it. Those who have opted in to the +1 experiment for search results, however, will be able to +1 directly from the product search page (rather than going into the product itself). The +1 will work as an extra layer of recommendation beyond the product reviews and will give a personalized element based on your contact network.
[via the Google Commerce Blog]