I've had 3 fail out of 12 over 3 years- 1 14W, 1 3-way, and 1 19W, all from Commercial Electric. All seemed to have the same failure mode- the glass cracked where it joins the xformer base, with evidence of scorching at the point of failure.

Not sure if that comes from the xformer operating out of range over/under and delivering unregulated voltage to the electrode, or if its from mechanical stresses in the glass at that point- the entry into the base is certainly the weakest point, especially if the spiral part was hand-torqued at any point in the past.

Overall, I am very happy with my CFLs