Interesting idea. I can think of a few different uses for it, although except for one, they're all fairly narrow uses.
1) Once you're happy with the amount of pillars/pends you have, send the rest to the bottom of your deck.
2) Get rid of cards that are redundant in multiples, as skyironsword mentioned (extra hopes, jade shields, flooding, etc)
3) Get rid of cards that are useless against your opponent (all those dimshields against fractal chargers)
4) Increase the odds of drawing something you really need/want by sending something else to the bottom of your deck. (The only card in your deck that will save your bacon next turn is that lone deflag, and you have 30 cards left to draw? Put something at the bottom, and now you've got a 1/24 instead of 1/30 chance to draw it, or whatever)
Are you able to target a spell in your hand with this? This could be interesting with something like holy light, or things like fire bolt against a reflective shield, or rage potions against a creatureless deck, for example.
@Chapuz: Unless I missed something in my reading of this card, while you can target your opponent's cards with this, it actually affects only your own deck. (i.e. you could target your opponent's lava golem, but it would put all YOUR lava golems on the bottom of your deck)
@iskelion: I think the cost for this card is probably about right, given what it does. I don't think I'd go any more than -1 cost to it, but I'd leave it as is.