Either the spray arms are blocked, check all three (don't forget the one of the top ceiling of the machine), or the filter may need cleaning (the worst culprit for this is potato!)
You generally should not have to swill dishes before putting in the dishwasher, however, as the water in the dishwasher is sprayed around the dishes it falls to the bottom of the machine, goes through a filter to catch large debris and is then recycled to spray once again. This water is then emptied, through the filter, and fresh clean water is drawn into the machine for the rinse cycle. Potato however does not "melt" well in the hot water and tends to clump in the bottom of the machine on top of the filter where it mixes with the new water and gets sprayed around again. This then dries on everything! very anoying!, definately swill plates and the saucepan if you have had mashed potato!
Otherwise check the salt and rinseaid levels are topped up.
Caroline, January 2009