I see the stuff you described and I'm always so thankful that humanity finally has public, anonymous dumping grounds for the worst of our id. It's therapeutic and, I think, healthy.
[1] A weak citation is here (but I bet you could find plenty more where that came from): http://books.google.com/books?id=Pye5IkCFgRYC&pg=PA853...
[2] http://news.ycombinator.com/item?id=1286253
[3] Unproductive in the sense that it isn't helping anybody. As is mentioned in the book excerpt I cited in [1], this isn't even "relaxing" people, except from exhaustion. It would be better if they were doing something which reduced their arousal.
It's just appeasing to some people to stop respecting rules and decorum for a minute. No higher meaning to it. There's some more serious stuff too, but honestly, when I want to read something intellectually stimulating, I don't go to 4chan /b/ or to the textbox where anonymous people write whatever.
EDIT upon looking more: I retract that. The companion cube song is oddly intact though.