When using the flaps, placard speeds exist for each flap setting stating the highest IAS for deploying. The also help reducing speed (but creating extra lift) but Mr. Boeing recommends not to use flaps as speedbrakes since the stress on the flaps is undesirable
I would hazard a guess and say most 737 operators pay lip service to the FCTM advice of "Normal descents are made in the clean configuration to pattern or instrument approach altitude...if greater descent rates are desired, extend the speed brakes."
While they may stay within flap airframe limit speeds (usually much higher than minimum manoeuvre speeds for the flap settings conccerned), there is evidence that pilots often cannot be bothered with excellence in flying, so they say it doesn't matter a stuff and go ahead and call for Flaps one through to Flaps Five while still descending and at speeds above the recommended.