When I was living out in Rome a few years back (2007 actually, so a "few" plus some), I flew with a stack of decks on my backpack from the US to Italy, no problem. Oddly enough, once I hit the EU, everywhere I flew made me check my fucking board. I ended up on a number of RyanAir flights, and they wouldn't budge on letting me fly with the deck strapped onto my backpack. It always showed up on the carousel in my destination, somehow, grip tape abused, sometimes totally fine.
Anyways, moral of the story is that unless the rules have changed, plan on a checked deck.