For the longest time there was a sense of unity; Anti-Bush, anti-war. Then a great deal of unity around the notion of hope and change after the economy tanked, slightly later the Occupy group was formed. However some of the more radical and vocal elements of the Occupy group were purged, and some only briefly drifted over from DU2 and then felt unwelcome.
I don't think many people go much further than general discussion, or the greatest page nowadays. One look at the most discussed threads, or the multiple (usually similar) threads about the 'outrage du jour' in GD suggest that in a vacuum, purged of radicals and dreamers, and starved of hope, that many of the participants are there to engage in bloodsport and bickering.
Chomsky's remark that The smart way to keep people passive and obedient is to strictly limit the spectrum of acceptable opinion, but allow very lively debate within that spectrum.... strikes me as fairly apt.
I also hope that some of the more non-mainstream groups pick up, and one lesson of history teaches that no-one has the foresight to accurately predict the event that ends up sparking a sea-change. However, the Labor group is kept pretty well stocked with news and info daily, and the socialist progressives group produces some great discussions, and has picked up some momentum lately. The Occupy group is one of the most unique groups on DU, since it is leaderless, and open to interpretation and reinvention as the Occupy movement diversifies, and similar movements rise and fall globally.