This seems to be a well known item in the knife making crowd. It sells for $55, but you should go to the store with the 20 percent off coupon you can find almost anywhere (like in your mail) and get it for $44 or so.
Note that people "move up" to a 2x42 belt sander after getting to like this thing, but the 1x30 gets a lot of admiration from the knife crowd. The Sears craftsman 2x42 seems to be the recommended item.
People use it for knife sharpening, but at best this requires an expert hand along with restraint and wisdom. Finer grits tend to heat up the knife and you can screw up the heat treat. Keep a bucket of water handy and cool the knife after every pass. Use an extremely light touch. Start out with knives you intend to ruin (because you almost certainly will).
The 500 (20 micro) and 1500 (9 micron) belts are the ones to use. The 320 grit belt may be used to "fix" a badly damaged blade. The 180 grit if for serious metal removal. At one time Lee Valley sold "blue Klingspor" belts that were highly regarded. Aluminum oxide are generally recommended, but other fancier materials are apparently worth the cost. If you are knife making a 40 grit zirconia belt is claimed to "cut like a madman".
Some people mount it on the wall (!!) so the cutting surface is horizontal and moving away from you. Sounds crazy at first, but actually working on a horizontal surface makes an incredible amount of sense.
Wear safety glasses! People say it is just a matter of time before an old belt breaks and slaps you in the face.
Lee Valley is recommended as a source for belts (aluminum oxide).
Tom's Knife Info / tom@mmto.org