I created an account just to see what it was and glean ideas. I spent about 5 minutes there and haven't returned. Every so often I get an email saying "your friend so and so is following you on Pinterest". My wife finds some recipes or party ideas there so I guess I've benefited from it's existence.
Same, my fiancee uses it but I didn't really "get it". She "pins" recipes, clothing items, furniture, decorating ideas, and things for our wedding that look neat. She explained it as she uses it to remember things, mostly, like kind of making a list and a central place to keep links to stuff of that nature. Seems useful enough for her, but I really don't have any reason to use it. The only people I know who use it are female, mostly her and her friends. Don't know a single guy who uses it.