I think that it would be wasteful to swap out the CFL's before they burn out. I think we don't properly appreciate the environmental cost of mining the terbium (a rare earth metal), of the mercury and manufacture of all the components that go into a compact fluorescent bulb (idem, a LED "bulb"), and the trouble in properly recycling these complex lights. It all screams green washing and consumer facilitation, much like how the proliferation of the triangular symbols on plastics helped the plastic industry convince us that it's OK to wrap _everything_ in plastic. Now light pollution is the worst it has ever been and it's only getting worse.