The popup is the biggest convenience of passbook imo. I have so many gift cards that go unused because I forget about them. To walk into a starbucks and get a reminder that you have a $5 card is incredibly useful.
For those who want to have Starbucks in their passbook there is a workaround. Not the most elegant solution, but here you go (you'll need an american itunes account):
http://www.iphoneincanada.ca/how-to/...da-workaround/