Well once you get so many, it's hard to remember that you've pinned it before, lol. I try to go back through mine every now & then, but I can't always see all of them for some reason & then I'll catch later that I've had something pinned twice for a long time.
My former's boss's wife got me hooked on pinterest. I use it for completely different reasons than she does though. I don't have the need to pin sayings or photos of models or stars. I only really use it for recipes, crafting pages, and crafting/household hints. That's the beauty of Pinterest though. It can be for anything you want it to be!