I've had CFLs all over the map too, from with lifespan in months to over a decade. When they fail, first they get dim, and at that point the transformer is also getting too hot. I pitch them then as a fire hazard (I've had 'em seriously brown the lamp socket).
On thinking about it, tho, CFL and incandescent lifespan was about the same in a given fixture or socket. I put one of each in several fixtures (both open and enclosed, some old, some new), and in the 13 years I owned the house, not a one of those burned out. Conversely anything I put in the open porch socket burned out in a few months, regardless of the season. The large open desk lamps, always in 3 to 5 years. How much a given light was used didn't seem to be a factor.