Doug Dyment also released the DAO stack recently. I love it, and now use it in place of Si Stebbins. It looks completely random.
That said... I used Si Stebbins for absolutely ages and showed the faces. The trick is to not spend too long doing so, and to not spread the cards smoothly. Mash them around in chunks, rather than perform a fine ribbon spread. You are, after all, only showing that they are normal cards (without actually *saying* so!). Don't make a song and dance out of it
I can't speak highly enough of the DAO stack. It's really easy to learn, too. I looked at the Breakthrough stack once and it hurt my head. DAO is, for me at least, much simpler to use.
T.
EDIT: Just seen Ian's post. Agreed. If they are *asking* to see the cards then there's a worse problem than an obvious stack at play. I don't think there's any harm in running through a face-up deck roughly, Charlier shuffle and go straight into something, though.
EDIT2: And if someone does ask to see them, after you've performed, give them a casual riffle shuffle and hand them over. Normal people don't know about stacks.