This is a great example of survivor bias. Just because you can list a handful of high-profile successes by no means discounts the arguments against Pinterest.
I can give you an equally invalid example of failure bias:
Groupon,
Friendster,
Myspace,
Digg,
Zynga,
etc
It's got nothing to do with survivor bias, it's just logic. The original commenter is effectively saying 'if A, therefore B'. I just listed several cases of 'A' where 'B' did not result. Therefore 'If A, therefore B' is not true.
Friendster failed because users migrated, ditto Myspace, Bebo and whatever else. Even Diggs downfall could be partially attributed to the ready made life boat of Reddit.
Google in 1998: "Their service is trivial, and can't scale."
Linkedin in 2003: "Their service is trivial, and can't scale."
Facebook in 2004: "Their service is trivial, and can't scale."
Twitter in 2007: "Their service is trivial, and can't scale."