Here is a wonderfully interesting article from Wine & Food Magazine on keeping your knives sharp. I sharpen mine a little everytime I use them.

Having a great knife makes cooking so much more enjoyable when you have this joy of cutting through something that’s so easy and effortless, plus it’s going to last you a lifetime and can even be an heirloom for your kids.
If you want to get the most out of that fancy new knife you bought—and have it last long enough to actually be an heirloom follow these tips from the experts.
Whatever you do: Don’t put them in the dishwasher.
The biggest mistake people make at home, according to Blanchard and Cox, is putting their knives in the dishwasher. Newer high-powered dishwashers can even warp the steel. You always want to hand wash and hand dry your knives.
“Use a kitchen rag or soft sponge be gentle.”
Remember that boning knives aren’t for … bones.
When it comes to knife work, bones are off-limits. Period. (And boning knives are designed for working around the bones and through the joints.)
People assume that Japanese knives can go through anything, that they’re like samurai swords. They cannot go through bone. They are finely made, like jewelry.
And please don’t try to cut through frozen food, either. That can damage the knife.
Ditch the bamboo cutting board.
What you’re cutting on is almost just as important as the technique you’re using. Hardwood is preferable. You can use plastic or composite rubber, especially when you’re cutting raw proteins, so you can just put it in the dishwasher. Bamboo is a little too rough.
Learn the difference between honing and sharpening.
Both are important. Honing, which you should do more frequently, involves grinding the edge of the knife on a stone to even it out. The process doesn’t sharpen the knife, but it fixes the blade’s alignment, which makes it feel sharper and cut better. Sharpening, on the other hand, involves actually shaving off some of the blade, and should be done a few times a year at home, or at a shop that professionally sharpens knives.
“”you don’t want to sharpen or hone your knife on anything harder than the steel of the knife itself,” says Cox, suggesting ceramic honing rods. “Hone your knife a couple times on each side – always use the same amount of passes on each side. Go ten or twelve. But if you’re going more than ten or twelve on each side, and it doesn’t go right back, then its time to sharpen.”
Incorporate oil.
Applying oil to a carbon steel knife will help prevent any oxidation or rusting, though don’t use any vegetable oils like canola or olive.
What happens with vegetable-based oils is they get rancid, so use Tsubaki oil, Camellia seed oil, very thin and neutral and you don’t need a lot of it. You can get mineral oil at the grocery store.
In many respects, you want to treat your knives like they are cast-iron pans.
For a stainless steel knife and carbon steel knife, you want to treat it like a cast-iron pan. Even for a stainless steel knife, some knives are high polished and contain nickel and silver. Humidity speeds up the oxidation process, causing the knives to rust, so you want to store them in as dry a place as possible.