I participate. After I put in a request to join, it took only about a day to receive the official invite to register.
It works like a online bulletin board. They suggest several topics for different boards, like favorite places and things, books worth reading, favorite recipes,etc., but you can create as many different ones as you want using names you like. You also instill a "pin it" button on your browser bar.
Then as you're on various websites and see something you want remember, you click the pin it button and save an image with your own note about it on the appropriate bulletin board. What's different is that it's focus is on saving a photo onto your board. For example, you're on allrecipes.com and see a recipe that looks interesting. You'd pin it to your "favorite recipes" board and what shows there is the photo of the recipe and it also saves the link so you can go back to it. Because it's photo based it's really good for things like scenery photos from travel locations, pictures of decorating ideas, fashions, color combinations,etc. Weddings seems to be a popular topic for younger women wanting to save images of dresses, decorating,cakes,etc.
While it's nice to have a place to save your own things, what's addictive is to scan through all the boards of friends or other creative people. You sign up to "follow" others' postings. If you link via Facebook you can see which friends are on PinInterest and opt to follow some of them or you can search for friend names. When you sign up, it also suggests a group of random others for you to follow.
So when you come back to the site,what you see first is a screen full of artfully presented images from all the photos others have pinned. Scrolling through those gives you lots of additional ideas and topics. So the more you follow people who's style you like the more things you'll see that you like too. Whenever you see something you like, you can then repin it to save it to your board too.
People who like to do crafts and decorating especially like it because they can follow other crafty people and find all sorts of ideas they wouldn't have found on their own.
I like to go to St. Maarten, so I've got a board for great island images, shots from restauarants I want to try, etc. I also have a board to save books I'd recommend and one for books on my "to read" list. What I do is pin the image of the book from Amazon or the author's website so I can read the reviews or background on the book too. It's been interesting to see how many others have repinned my books to their board. I've repinned several recipe ideas, some travel images and some fun sayings that make me smile.
I guess I need to start a "timeshares to visit" board.