The mortgage crisis is also an opportunity, as this news article from Miami shows. Take Back the Land, which a few years ago had organized a long-term protest tent city called Umoja Village (watch a short documentary video on the Village here), is back with Take Back the Houses, a plan already underway to reclaim the houses left empty by the bubble's collapse with those in the most need of housing. Read a news story from the mainstream Miami press here.
For more info on the campaign, see the Take Back the Land site.

Also very interesting is the theory of "post-gentrification" underlying these actions. Max Rameau's Gentrification is Dead is essential reading for any discussion of contemporary urban struggles.