Upgraded to iOS 6 today and wanted to play around with the new Passbook app but I ran into an issue with it connecting to iTunes. Pressing the App Store button in the Passbook app opened the store but it would just show a generic ‘cannot connect to iTunes’ error. The App Store on my phone was otherwise totally functional.
Here is a link to an Apple forum post with a fix for the issue. The problem in the forum post is for an iPad 2 having App Store issues but it worked for my Passbook/iPhone issue too.