On Comparative Advantage, Imperfect Markets, and Boston Weather

Seth Gitter asks, very sensibly, why did I spend time shoveling snow from my own roof a few days ago, rather than relying on the invisible hand to do it for me?  Shoveling is, after all, not my comparative advantage. 

His speculation is right: I could not immediately find someone else to do it.  Everyone my wife and I called had a queue of roof work to do.  (Question for class discussion: Why didn't the price rise to clear the market?)  Eventually, however, we did get to the front of the queue, so I could get off the roof and return to teaching and writing.  But not before the huge ice dams pulled down a gutter on one side of my house.

By the way, as I look out the window right now, it is snowing again.  Anyone know of any job openings for middle-aged economists in warm climates?  Maui would be nice.