Honestly, the kids are so excited to be going to the computer room that they generally get there and get seated before an adult has time to monitor it. Being "left out" and alone at a computer is rather the goal of most of our kids, but they know that sharing a computer is the way it will be, so I can't say we've had complaints.
I've taught all our workshops at one time or another and I have to say who sits next to whom to giggle in the movie theater, or who gets left off a team in the games rotation is a bigger social issue. I've never seen anything like you described surface in the computer lab.
Peace,
Lisa