The local market conditions are what seems to determine the abandonment decision. In a region where the job and real estate market is doing anything better than "a little soft," I would surmise that abandonment makes no sense at all.Link (Thanks, Jason!)
However, at a certain point, in a weaker region, with declining neighborhoods, certain lenders might make the decision to simply walkaway from a large swath of (potential) real estate holdings, on the simple basis that it might be cheaper to do so.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.