Maintaining a dishwasher
I'm surprised with the frequent complaints about dishwashers suddenly not cleaning well, that many people mention changing detergents, but hardly anyone mentions checking or maintaining the physical spray arms and water delivery.
I have a six-year old Maytag that was the top-of-the-line at the time. It was never a great machine, but generally performs adequately. However, three times in those six years, the top rack cups and glasses would start coming out with lots of dried grit (looked like salt and pepper stuck on, esp towards the deepest parts of the cup.
Since the mechanisms of the washer are pretty basic and the same - water, heat, motion - all three times I did a simple test to see if the spray arms were working. I'd open up during a cycle and line up the arms, then close up and let the machine restart for a few seconds. Then I'd open up again and see if the arms had moved. In all three times, the upper arm had basically stopped moving, indicating not enough water and pressure was flowing through, and thus most of the upper rack was not getting a strong spray anymore.
Once it turned out the plastic channel in the back that routes water to the upper arm had gotten partially dislodged, and I just had to snap it back. Two times, undissolved food and residue had clogged the spray holes, so I cleaned out the holes with toothpicks and a screwdriver. After remedying the water delivery, the spray arms started moving again, and the upper rack items started getting clean again.
I feel these are common physical things that can degrade many dishwashers regardless of brand, and probably one of the first things to be checked if a dishwasher performance starts to degrade suddenly and gradually. Just wanted to pass this suggestion on to others...