Yeh I am a heavy user thanks to apps like Lemon Wallet. Allows me to add all my loyalty and membership cards to passbook. Currently have:
Delta
Fandango
Starbucks
Target
Walgreens
CVS
Billguard
Gym Membership
2 Museum memberships
Drivers License
Starwood Card
Marriott Card
3-4 other loyalty cards
So it is pretty useful after all, if you live in the US. To the rest of the world it's pretty much useless so far. It would probably catch on faster if it was a more universal tool, that wasn't locked to iPhones.