We give our dishwasher a clean with one of those cleaners that go in that Traveller is talking about and run it on a long cycle with no dishes.

I agree it sounds like the spray arms are not working well. I once had a load come out dirty and discoverd a piece of cutlery jammed in stopping the arms from spinning at all.

I didn't realise they had little holes in them, might give ours a good clean out too!