"All four European Free Trade Association (EFTA) member states – Iceland, Liechtenstein, Norway, and Switzerland – have signed agreements on association with the Schengen Agreement, even though they are outside the EU"
You usually don't even have to show your passport when boarding a plane in Zurich as long you're flying within the Schengen area.
I think that's the case in most Schengen airports now.
What can happen is that you're checked by customs at the border. Since Switzerland is not in a customs union with the EU. Generally speaking, though, it's free flowing.