We had a pretty good discussion today, especially on the distinction between the Schumpeterian and Kirznerian entrepreneurs (perhaps too much on Christiansen).  Ladies and gentlemen, the Kirznerian entrepreneur (emphasis his):

For me the function of the entrepreneur consists not of shifting the curves of cost or of revenues which face him, but of noticing that they have in fact shifted — Kirzner, Competition & Entrepreneurship, p. 81.

For further explication of the differences between Schumpeter and Kirzner (beyond what’s on pp. 79-81), see this piece by Don Boudreaux.