Brevity points to a new wrinkle in the world of literature and the internet: avoiding the appearance of nepotism via social networks. Jon Tribble, the editor of Crab Orchard Review posted a message on his Facebook page advising those who wanted to enter any of their contests to "unfriend" him, to avoid the impression that he might favor entrants in his social circle.
I'm not sure this is entirely necessary. The definition of "friends" online is strained to say the least, and there's no guarantee that a mere Facebook connection or Twitter follow can make that much of a difference. But interacting online in any shape or form could give someone the impression that they had an in with an editor or contest judge. I can picture the cover letters: "I really enjoyed that link you posted on Twitter the other day. And those vacation photos from Jamaica look great ..."