Yeah, the chart tells the story. I think they had a difficult time picking up traction. They did a kind of pivot recently when they added the ability to stamp books, music, TV, movies, iOS apps, etc. But when I used the app it was confusing and scattered.

I read a blog post by MG Siegler about Stamped a few months ago (http://parislemon.com/post/28144863354/stamped-is-it-worthy), but didn't buy his enthusiasm. Stamped seemed like too difficult of a concept/activity for the masses to understand and too broadly marketed for early adopters to get really excited.