A blog lets you define yourself, whereas on a social network you are more likely to be defined by others. […] Sure, a blog is dependent on the links you point outward and those that others point in; but it has its own independent existence in a way that no amount of messaging and chat and interaction on a social networking site can match. A blog is not necessarily better than a Facebook profile, nor is it worse; it is, simply, different. […] It is, as the journalism scholar Jay Rosen puts it, “a little First Amendment machine,” an engine of free speech operating powerfully at a fulcrum-point between individual autonomy and the pressures of the group. Blogging uniquely straddles the acts of writing and reading; it can be private and public, solitary and gregarious, in ratios that each practitioner sets for himself.
— scott rosenberg. well put.