I'd like to consider myself a digital man about town. You know, I think I generally get the Internets, seeing as how most of what I've done for a living in the last 14 years or so has involved it in one way or another. I didn't "get" Twitter at first, but as it turns out, it was more that I just didn't have much use for it. Now the great quasi-mystery is Pinterest.
I say quasi-mystery, because I have some theories about its popularity. It tends to be a "girl thing." That seems weird at first, and a lot of people have made theories about why that's true. Most of those theories talk about branding or momentum. I think it's the design.
I wish I could find the article or paper that I read years ago about the wiring difference in men and women, but it goes something like this. A study was conducted about the way that people navigate. Men had a great tendency to think spatially, like a map. They would take freeway A to exit 2, turn right on street B then left on street C. Women, by contrast, had a tendency to think visually, using landmarks. They would get on the freeway, exit where the tall Holiday Inn sign is, turn right toward downtown, left at the library. Mind you, there's a spectrum between these thought processes, but these are the tendencies between the sexes.
So apply that study to the design of Pinterest. It uses collections of images as links to different things on the Web, arranged in a fairly random set of columns. It's very visual compared to, say, a big table of links nested in a hierarchy. I've seen it compared to scrapbooking, which is also something that tends to lean very female.
The idea behind Pinterest is actually not new, sharing links with others. The one-ups for this service include a subject agnostic approach, so you can share links for anything and see them grouped together. The visual nature of it is the bigger win, even if the appeal tends to lean toward women.