I know it's not an instant-kill, but as milling goes, it's a nice idea. You're not damaging them directly, so the ability is useless. Either you'll continuously eat at their deck, or they'll toss it altogether. I know blue can be powerful, as I am seeing with my current Mill deck, but it's also one of, if not THE slowest, color in Magic. I rather like playing creatures and spells every turn than just land, waiting for my opponent to react. I like to FORCE the reaction.