Ubergeek the problem with that circuit is you need a rather robust snubber, or you're going to fry the igbts. Mosfets won't die immediately but will fail eventually unless they can handle the avalanche current and energy.
Triacs do not have this problem because they turn off at zero current, thus they don't need a snubber except for rfi reduction.
If Larryboyz is trying to pwm an ac load off the mains, any energy stored in the inductance of the mains is dumped into the switch when it opens.
depending on the frequency and all that, the power that has to go somewhere can range from 1 watt to 1000.. and beyond. its not impossible to dump the energy back into the mains but the practical thing to do is just put a big capacitor across the mains, and a snubber across the switch.
the problem with that being, the capacitor must be able to handle a significant amount of rms current. significant as in about half of what the load draws.