The most surprising thing I've seen in 2009, courtesy of Etherpad
I've been wanting to play back the writing of an essay for years.  Since Etherpad saves every keystroke, I convinced the founders to add a way to play them back.  "Startups in 13 Sentences" was the first essay I wrote on Etherpad.  Now I'm going to write all of them on it.Playback is just one little feature of Etherpad, but think of the implications of this alone.  Among other things it will make cheating impossible in classes where students write papers, because now you can finally "show your work" in writing the way you do in math.