It is of utmost importance that you steel your knives on a regular basis after they have been sharpened. I recommend a ceramic steel, like the one for sale on my Web site, especially for Japanese knives. Whatever kind of steel you have, if used regularly, the edges will last a long time.
Here is a useful steeling demonstration from Mr. Alton Brown from the food network. I prefer alternating each stroke on either side of the steel, but you'll get the idea. http://www.youtube.com/watch?v=lRUYAgrsoLw