Comments
What social aspects are there of a blog? Well, since the rise of Facebook and all, 'social' has become somewhat like a buzzword. All human activity is social in some way. But hey, definition that you get right away is the best definition.
So, we have comments as an obvious example. In my opinion, comments are unnecessary for blogs. For those people who comment on blogs, you should start a blog and get your own voice. Get a proper online identity, not a fragmented one.
Because I'm writing a static blogging system, having an in-house commenting system means regenerating the whole website each time a comment is posted, which is a huge down for performance.
If you must use commenting, using an external system such as DISQUS is much better.