Wikipedia has a good article on dishwashers - when the machine runs bits of food debris and limescale deposits are sometimes suspended in the water - they can get baked onto the crocks at drying time.
You might wish to clean the filters and spray arms - buy some cleaning tablets and run one or two through the machine - always use good quality rinse aid - top up the salt reservoir and avoid the "multi" tablets unles you live in an area with very soft water. Rinse off the worse of the food debris before loading - make sure the water can reach all surfaces to be washed when loading up.
Above all rinse aid - it helps the crocks to drain before drying - any crud in the water should run off.
Glassware is often subject to "hazing" which is a different thing to bits of baked on dirt.
Good luck...
Peccavi
March 2010