Wikipedia has excellent paragraphs here...
http://en.wikipedia.org/wiki/Dishwasher#Rinse_aid
Rinse aid and Hazing of glassware are good bits to read.
Always use good quality Rinse Aid and wash off as much loose crud from the dishes as you can before loading them else it breaks down into tiny pieces and gets baked on during the drying cycle.
Peccavi, April 2009