Usually it's a dominance move used more in play between two dogs, than anything else. If my dog is just goofing around with one of her big buddies, she'll even do it. I don't make a big deal about it as it is an occassional "thing" mixed in with the play.
Now, if she were to do it to me, she would get a verbal "hey" in a low tone, a firm, but not angry, "look", and I would move forward towards her...just enough to claim the space she was in while she was doing "it".
Okay Doberluv, you don't need to post that picture of our dogs at "play"!