They have become a necessary evil, so to speak. It is one time when the consumer is dictating to us regardless what our individual preferences/opinions may be.
Personally, except for "like" buttons, I feel loading pages with social network plugins just slows down the page and, depending on the site, provides irrelevant information.
IMHO, we have all become coerced promoters of these mega-million dollar social sites. And you have to admit it is bad when that ubiquitous "f" is in a print ad as if you could click on it.