it all depends on your weight vs. the feel of your bed. if you are 300 lbs. with a soft bed then yes its bad...also you may find over time that you get neck stiffness because sleeping on your belly means your head is always turned to one side. basicly..as a stomach sleeper you want a bet that will support you correctly...make sure your spine is aligned correctly. if you live anywhere from New Jersy up to Nh go to your local Sleepys and as a sales person...we are trained heavily to know these things :-)
Some of the side effects of sleeping on your stomach include increased wrinkles because as you dream, you're face gets more crushes and sexual problems between you bad you're partner. However, the position is useful because it alleviates abdominal pain.