There are far more cons than I would have expected for a company that is doing as well as Pinterest is externally. I think it is a core product that resonates with a large audience, but these problems will hold Pinterest back from becoming more than it is.
The quality of management in engineering is mind bogglingly poor. It hits a level of incompetence I haven't seen at any of my previous companies. I've seen individually bad managers who soured their piece of the company before, but this is systematic. The exceptions are two leaders (previous managers from Google) who do a good job - but they are not enough to turn the tide and keep the other managers inline. I wish we were measuring good v. great, but we're measuring incompetent v. good.
I agree with the other reviewers on discrimination and political infighting. That definitely happens, it's just a matter of how close you are to it within the company. My estimate is about a quarter of engineers are pretty close to it. Those are just the byproducts of the above stated problem. Other symptoms include teams out of sync, a low experiment/product success rate, unreliable data, unclear seniority levels, regular reorgs, people leaving without announcing or goodbye send offs, low psychological safety index, haphazard product innovation, and wild variations in resourcing compared to project size.
For an experienced engineer, I would personally recommend waiting for a VP of engineering to be hired before joining. They'll have a direct impact on solving/aggravating the above problem.