I just read Michal Coughlan's piece, Thinking Deeply about the Shallows in which he discusses ideas from Nicolas Carr's book, The Shallows: What the Internet Is Doing to Our Brains. For me the main issue he is raising is whether the young learners of today are losing the ability to do vertical learning ("singular, in-depth focus on one topic") because they are more immersed in horizontal thinking "(multitasking possibly in connection with networks of people").
Personally I find that I tend to read blog posts and tweets more often than I write blog posts myself. This is definitely because of the time and deeper thinking involved in producing a reflective piece as contrasted with finding intriguing snippets of information and retweeting them or putting interesting new websites in my Diigo account for further analysis. (Unfortunately that further, deeper consideration often never occurs).
I think as educators we need to ensure that learners practice both types of learning. Some learners need to learn to utilize social networking sites for educational purposes while others need to learn to do read, reflect, and write. Each type of learning serves a purpose.