I just seen this "dancing" in a video recently... i've never even heard or seen it before.. I guess cus it's in the US.. i've been to several concerts recently and there wasn't any of that crap.
I find it fun. That's all I can say. I find it a lot more fun to do that then bump into someone else repeatedly. And I only do it when I go to hardcore shows.
Except when I two-stepped during Bodom's sets when they opened for Lamb of God