Once you Pin it ANYONE on Pinterest can see it and Re-Pin it and so on and so on. It's a quick way to get all the incredibly ingenious Instructables out there into an audience that may not even know Instructables exists.
Instructables gets fresh brains to pick
Members get even more new creations to oogle & try out.
Your Own/Favorite Instructables get views from not only the Instructable members who have are interested in it, but EVERYONE on Pinterest who may have an interest in your idea, Plus your FB friends.
It's also a much better way to save your bookmarks, because you have a picture to remind you what the link is for.
So, if you have a friend on FB who uses Pinterest, ask them to send you an invite. If not, just go to Pinterest.com and request an invite. They will send you an invite, in about a day or two (that's how long it took mine) and then you are ready to get the word out about your favorite sites, like Instructables!