Here's info. from the Chef's Choice website on dishwashing knives:
Washing sharp knives in the dishwasher can be hazardous to the knife, the dishwasher and the cook!
It is too easy to reach into a dishwasher and get a nasty cut. Sharp knives can knick plastic-coated wire shelves and other utensils. The force of the water can dull knife-edges by pushing them against shelves or utensils. The combination of hot water and the chemicals in dishwasher detergent can leave stains on stainless steel cutlery that comes in contact with silver or silver-plated flatware or copper. (These stains don't effect the knife's performance.)
Occasionally my "kitchen helpers" have been known to put my good knives into the dishwasher. Once I even found a paring knife, which had been lost for months, "hiding" on the floor of the dishwasher. Who knows how long it had been there? (I use modestly-priced paring knives because they have such adventurous lives--they are more likely to be broken or chipped than any other knife in my kitchen.)
That being said, I keep my dishwasher set to "energy-saving air dry" and I always use a gel dishwasher, which is less abrasive than the powder kind. (Some powdered dishwashing soaps may actually use sand as the cleaning/abrasive agent.) I wouldn't recommend knives in the dishwasher, but if they are apt to creep in when your back is turned, you can do something to minimize the problems.
Life is never perfect, alas! And I never turn down offers of help. (Although I usually try to handwash all the knives before the help arrives.)