Personally, I love social sharing buttons. Without them, I believe sharing of pages (especially blog posts) would decrease drastically. I am a fan of minimal design trends, omitting everything but the essential from a page and I respect why some people have strong feelings on the subject.
I think we, as the tech community need to find ways of facilitating the needs of everyone in a way that's natural. I like the idea that I can share to Facebook (with my close friends) to Twitter (with my followers who may or may not know me in real life) and I can also see the use for Google+ and LinkedIn for sharing with professional contacts.
What does need to die however, is the overuse of social sharing buttons. I've been to way too many sites where you have a social sharing strip before AND after the article and then a floating sidebar to top it all off.
Would love to see a report from KISSMetrics / Mixpanel on how effective the various implementations of social sharing buttons are.
Anecdotally, I've been using Mountain Lion for just over a month now and while I initially thought the OS level integration with Twitter and Facebook would be really useful to me, I've hardly needed to touch it wheras on mobile (Android) I usually go with the browser's built in sharing function. I'm still not sure if we're seeing a shift towards mobile rather than people just consuming content in multiple ways, but if that were the case I think OS level sharing is going to gradually become more important maybe even overtaking social sharing buttons. Also, as an aside, saw Kera a few days ago, looks really awesome.