Quite an odd spectrum of replies here, this is the first place I've seen anyone who wasn't absolutely in love with their Nike boots.
I bought a pair of Vapens last year, got size 10 because that's all they had near my size and I needed boots right then. My actual size is 10.5, I sometimes wear 11 for casual/street shoes and occasionally size down to 10 for cleats or running shoes. Anyway, when I first put them on they were awfully tight, but I wore them all evening around the house for a few nights, and then on the ride up from SC to WV, and I honestly forgot I was wearing snowboard boots a few times. Seriously, these things are as comfortable as my Jordans, you can wear 'em all day as long as your feet don't get too warm. The 10's didn't really pack out, as much as they expanded just enough in certain areas while still having a nice snug fit overall. If I sit with my feet propped up high for an extended period of time, they start to feel a little tight, but I love the snug-ness.
To sum it up, I got Vapens a half-size down from what I normally wear, and wore them as much as possible before my first trip in them. They are now as comfortable as basketball shoes, give great board feel, are nice and light (as far as snowboard boots go), and have a comfortably snug fit (they feel like they're a bit small when you're first putting them on, but within a few minutes you forget you're wearing them). I can't recommend them enough, and yes, go one half-size down.