Some people are concerned that this is an example of Google using its dominant search engine status to push consumers into Google+.  I'm not buying this; if I care what search results my friends "+1ed" I'll ask them, it isn't enough to push me to Google+.  I do use Google+ already, and I don't see this being a huge mover of people.  A related complaint is that Google is not utilizing similar search results/info from Facebook and Twitter, so that it is essentially an anti-trust issue.  I'm not convinced on this point either.  Google has attempted to use results from both of those companies in the past, and they both refused Google's offer.  So now they are upset when Google uses it's own social media to drive search results.  That seems a little like a kid not wanting to share his toy, then throwing a tantrum when he sees another kid playing with his own Stretch Armstrong.  I do agree with wolfkin_'s point about the default setting including Google+ driven results, which requires users to opt-out instead of requiring them to opt-in.  At the moment the opt-out is very easy, with a button at the top of the search results page, and hopefully Google will never go the way of Facebook and hide settings in a confusing menu of account settings.