One bit of Google gossip that has largely flown under the radar thus far, should the rumors turn out to be true about Google working on a third party commenting system, could have a large impact on organic rankings.
Most of the discussion regarding this commenting system has revolved around speculation that Google is trying to further force people away from Facebook to start using Google+ as a daily part of their online lives. While undoubtedly true and a big part of the reason Google decided to build this tool, search engine optimization (SEO) implications could make this announcement even bigger than most initially thought.
Hello Authenticated New Content
This new platform would give Google an incredible tool to curb the endless comment spam manipulating their algorithms. Sites that use other commenting systems have historically given Google a difficult time in figuring out whether user content should be considered legitimate or manipulative, and Google has implemented a number of ham-fisted responses to dealing with them (i.e., giving the content within comments less value when compared to other content on the page, recommending sites no-follow links within comments, etc.).
With this new source of content coming from verified Google profiles, Google should be able to assign a score to the author of each comment based on their overall Google activity and weight the value of the comment accordingly.
If Google implemented something along these lines, it would require spammers trying to influence Google's algorithms through commenting to first build up credibility with Google. They would need to participate in other Google products like YouTube, Gmail and Gchat in order for their author profiles to achieve a high enough trust level to warrant Google giving the comment any weight.
So Long "NoFollow" Comment Tags
Assuming that Google does use the commenter's profile to verify that the author is a legitimate person, it would open the door for Google to allow links within comments to pass juice to the sites to which they link. It goes without saying that legitimate commenters will still want to push sites they are invested in, but it should be relatively easy for Google to create some rules that flag frequently posted links from the same user over a short time period and devalue them.
Meanwhile, links from commenters that appear on topic, have good click-through rates (CTRs), and haven't been posted an inordinate amount of times could be a fantastic new set of data for Google to incorporate into their ranking algorithms.
Overall Site Boost?
Due to potential antitrust issues, it's probably a stretch to think Google would ever outright say or even imply that sites using their commenting system would get preferential treatment in their algorithm. That said, Google still could implement a small change in their algorithms along these lines.
The amount of insight Google would gain about sites that utilize their commenting system’s demographics could provide an incredible amount of clues as to whether pages are useful and the type of people who may find them useful.
Whether or not these ideas come to pass, the chances of Google's commenting system being a new signal in their ranking algorithms should be enough to encourage many webmasters to consider switching to this system from whatever they currently use. Naturally, speculation like this is something Google isn't likely to discourage as it seems that pushing Google+ usage is a huge priority around the Googleplex these days.