WARNING: You need to have a strong stomach to try today's suggestion!
The process is very simple. Depending on your model, there are one or more little filters and compartments that you can remove the cover to and clean out the (ew, gross) gunk behind. The directions had warned me that this was a pretty gnarly job and boy was that the truth! Wear gloves. Hold your nose. Avert your eyes.
Anyway. I removed what I could--carefully prying things open, not forcing anything--and soaked the pieces in bleach and water. I was also able to unscrew the spinning sprayer from the bottom of my dishwasher to reveal areas underneath where I found something that will remain nameless--because I have no idea what it was, but it sure was jammed under there and it sure needed to go! Then I put it back together and ran the hottest/hardest cycle that I could with a mug of vinegar sitting in the basket. I actually did this two times, after wiping a few areas inside with a bleach soaked sponge. There were some spots that really needed the bleach due to a build up of mold that I had not even noticed (told you this is gross)...
I also checked each little hole in the sprayers for debris and cleaned that out as well. Use Q-tips or pliers or whatever you have on-hand. I keep an old toothbrush under my kitchen sink for jobs like that.
Anyway, let's just say I feel so much better knowing that there is nothing living in my dishwasher and it can do a better job of cleaning my dishes!!!
Extend the life of your dishwasher and try this idea, too! It won't be fun, but you'll be glad you did it!!!
**October 2012 Update... a year later!**
A couple of weeks ago our dishwasher made this strange "I am dying sound" and then quit working before it finished draining... Very disappointing... not something we really wanted to be dealing with at that moment, not that anyone would want to deal with that EVER... anyway, let's just say that putting the above suggestions into practice became VERY IMPORTANT!!! We took apart the filter and discovered broken pieces from when the crockpot lid handle and a wine glass had been broken several months ago... there were little pieces stuck down inside there and they were ruining the dishwasher! We cleaned and cleaned and tried not to throw up and when we were done the dishwasher ran again! Not sure how long it will last, but we'll take it for however long we have. When we were reading about what to do when this kind of thing happens, we discovered that if you allow something like this to go on for too long you can burn out your motor and have to replace the entire thing... so
Moral of the story is: Clean Your Dishwasher. For realz.