I've read up on this a while ago. Apparently, you shouldn't sharpen the knives with a whetstone or similar very often, instead you should steel the knife lightly before using it, and maintain the edge that way. Then you re-sharpen every 6 months/year depending on how much use the knives get.
If they're dull, do a proper sharpening and then before you cut anything, give the knife a quick steel, cos the edge will "creep" slightly while it's sitting idle. There's no point sharpening a knife on a block and then not maintaining the edge while it's being used. A couple of swipes on a steel is enough to make a good edge last a long time
EDIT: This is the article I read -
http://forums.egullet.org/index.php?showtopic=26036 it's just one massive forum post - goes into a lot of detail. I read it all, and I'm better off for it
