I remember when I read people saying to wash your hands before handling cards I was like, "Pssh, bunch of wackos" but it is really true. I often find myself in a dilemma about practicing handling of cards. There's so many different varieties of stocks and finishes that you need to practice to get things right, and yet practicing things you're not used to is a sure-fire way to ruin the cards.
Also, although I really like ambitous card routines, I always get a little sad when people take a Sharpie to a card. Even if it's just a regular deck.
Probably the dumbest thing I've done is that at present I just have all my decks stuck in a little wooden drawer. I need to find somewhere less hazardous and where they don't need to be stacked four high.