Well Fel-pro had a bad run of them a few years ago, the metal was too soft and they would stretch out after a year or so and blow the head gasket.
An in the mid-90s Ford had some that were too brittle and the heads of the bolts would pop off, and blow the head gasket.
On the whole however they are a much better fastener than the old style. They provide a much better, more even clamping force with fewer issues than traditional bolts. Just don't let yourself get pulled away while torquing the head, and don't lose your place. And get OEM ones, not after market. Head bolts, spark plugs, and brake pads are the only places I really push OEM stuff every time.