The app looks good, and you've made a lot of great design decisions. However, it took me a little too long to figure out what the idea was. Three suggestions:
'shop. save. share' doesn't tell me enough right off the bat. Maybe users who aren't logged in should get a 15-word blurb ("Postabon allows you to find and share deals. Check out the (link)introduction video.(/link)")
I didn't notice the introduction video side-tab until my third glance back at your site- most new users are going to totally miss that.
The 'about' page had more words than my eyes were comfortable with. Cut the word count in order to space the text out more. And some hyphens show up as em-dashes in firefox, not sure what the deal is there.