When I click the Appstore button in Passbook I receive the error: "Cannot connect to the iTunes store"
Gotta Be Mobile provides a great article detailing the issue with Passbook and a fix. I've reposted the fix from the article below:


  
  First, head to the Settings in your iPhone.
  Click on General.
  Next, head to Date and Time which is down the list.
  Once you’re in there, you’ll want to change Set Automatically to Off.
  Go to Set Date &amp; Time.
  Click on Today’s Date. Once you do that, you’ll be given the option to change the date.
  Move the year one year forward one year.
  This will prevent the error from happening. If you wish to change the date back to the real date, simply set Set Automatically to On and
  everything will return to normal.
  Head into Passbook and click the App Store button
  


Something about moving the date up might be expiring a certificate or just the adjustment of time back to correct seems to make passbook behave better.