We also used power backs on our DC9's and 727's only, and then only if the ramp was "not contaminated" - no rain or snow. Although in the winter, we'd sometimes have our 747's with the inboards in reverse and a "wee bit o' power" to help the tug over the icy bits of the ramp. I must admit to being one of those who voiced concerns about engine FOD when we adopted the power back procedure, but I can't recall ever losing an engine to a power back FOD incident or stall. As "mustangsally" pointed out, it didn't take a ton of power to get the beasties moving, so as long as the oil temps were in the green, or yellow and rising, there was no harm to the engine. All you had to remember was that to stop after the power back, it was forward thrust not brakes - not unless you want an embarrassing view of the sky and a "hats-on" interview with the the Chief Pilot.