Seems OK but
Not terribly useful for me. YMMV of course but I don't need to fly, Target and Wallgreens aren't in Canada and I don't drink coffee so I never go to Starbucks. Others might find it useful but for now it's staying in my Retired Apps folder. I'll check it every six months or so but for now it's just a placeholder.
I do want to comment on one thing. Apple used to be known for intuitive designs. How something works used to be obvious, witness the 3 year old I saw on YouTube that 'got' how to work an iPad in a few seconds. Passbook is clearly not in this league. You open it and get a screen saying how it's the best way to get this that and the other but no indication how. There's a button at the bottom for the AppStore but I don't want to go to the AppStore, I want to get the tickets and coupons you talked about. How about a couple lines of text explaining how this works? How about instead of an AppStore button if the big colored icons for Boarding Passes, Coupons, Store Cards, and Tickets were buttons that took you to the part of the store where these things are? That's where I tried to click at first.
It's a fine idea but Passbook was rolled out half baked, much like the Maps app.