Over on Epicurious, Siobhan claims that using a magnetic knife rack will dull blades less than a knife block:
"It's smart to use wall space however you can: Hang knives on magnetic strips mounted to the wall (they don't get as dull as when you store them in a knife block). And install shelves over doorways for extra storage."
I disagree with this, as a good quality knife blade is not going to be dulled by a block of wood just by sliding the blade in.
You could easily argue that pulling a knife off of a magnetic strip every day would damage the blade.