guvnornot directly, but sharper points on magnetized objects focus the magnetic field. So the sharp edge of your knife is more likely to pick up magnetic dust (like little bits of steel left over from sharpening), which will sit flat against your edge effectively dulling it. I'm not sure if it's a big enough deal to a home cook, but I would be very surprised if a pro used a magnetic rack to store their blades.
tyler256I personally recommend wiping off an edge after sharpening(or even honing) regardless of whether it's magnetized or not; most of the metal dust will get wiped off on whatever you're cutting first. Most people don't seem to care or notice though.