I just send mine out to be sharpened. I think it's around $4/blade and I've been happy with the results. I have not ever tried to sharpen them myself, but have heard from those who have bought "home" level machines that it's a pain in the butt and not very good. I think that the machines the professionals use are very expensive ($1,000 or so, if I am remembering what I heard correctly).
How well sharpening works not only depends upon the machine, but also the person doing the sharpening! I just send my blades and clippers to the professionals. Check out http://www.bladeguyz.com
Friend was selling out his professional blade sharpending business so my husband purchased it for his retirement job next year. We have been doing quite a business thus far. We charge $3.50 plus shipping and handling. Glad to do them. www.crescendo_acres.tripod.com. PM me if you would like to know more about us. We are also in the process of becoming a dealer in NH for Double K's.