I cannot really comment on how efficiently it can be used for SEO, but am pretty sure google wanted to create a broad social network just like facebook, for if(when) social search is a big portion of how content is discovered.
It clearly did not work out for them, despite their efforts for force it upon users.
If Google wanted G+ to be like Facebook, they would have built it on different fundamentals. It's funny that on a forum full of people who believe that Google is all-knowing, all-seeing, and all-powerful you guys believe that Google has utterly failed with G+ and has no idea what they're doing.
I don't know if G+ has failed or not, but it was never supposed to be Facebook. If Google had wanted to build Facebook, they would have based G+ on symmetrical relationships (you friend me, I friend you), not the asymmetrical relationships of Twitter (you follow me, I don't have to follow you). Now, people who jumped at this and said, "aha, they're twitter 2.0!" are on the right path, but they aren't thinking broadly enough.
Google+ isn't Twitter. Twitter's focus is on the delivery of short broadcasts (Twitter is essentially the layman's version of RSS feeds with the ability to brand them and discuss them). G+ is focused on the delivery of content and the creation of online personas that can be attached to articles. Think about it. Google didn't want to let people register pseudonyms. Why? Because they want to know who writes what and they want to be able to tie authors to their content, their social media accounts, their videos, and their websites. Google has backed this up with rich snippets, which allow brandable photos of individuals to appear next to articles they've written. They've added the rel=me tag and the rel=author tags all for the same reason -- identity.
I don't think Google ever intended G+ to be a true social network. I think Guerilla is right to say that they intended to make it an authorship network. They tried this before with Knol, which never worked so now they're trying it by giving authors a platform to brand themselves with videos, pictures, introductions, and automatic links to everything they've ever created.
Google just let everyone else label it a "social network" and went with it. I think they were afraid to tip their hand too early. All I know is they've gotta be doing something right because Facebook rolled out asymmetrical relationships ASAP when G+ launched. A further hint that this is the path Google is taking --
Facebook + Journalists | Facebook . Imitation is the sincerest form of flattery.
We won't know whether this gamble worked until (if) they hit a critical mass of authors. Once that happens, all these dormant G+ accounts could come alive as people start just following authors and topics they're interested in directly. That's why I don't think Google is too scared of their low levels of engagement right now... they're just laying the foundation for something bigger. Maybe.