I’m in the US and know it exists, but I don’t know anyone who uses it. It seems like it’s used predominantly by women to collect and share photos taken by other people (e.g. photos of clothing, makeup, fashion models, crafts, weddings, food, etc.).

The fact that I don’t know anyone who uses it does not imply that Pinterest is unpopular. I just know so few women.

Pinterest is relevant and generalist enough to be useful to most people, allowing different usecases from a free cloud storage of pictures to a social network.

Reasonably well-known in Brazil among crafts-interested general audience and related areas.

I don't know anyone in the US using Pinterest. It seems like a search engine gaming scam to me.