Pinterest: Caution, Addictive

I've stumbled upon a new sight that is fun to browse through called Pinterest.  I don't completly understand it, but you can "pin" items from various places online to your virtual "bulletin board".  For instance, suppose I was trying to pick out a new quilt pattern.  As I found them at various sites I could pin the pictures to my board and then view them all together.  They link to the original site.  Others can also view your boards and can comment or "like" your pin or even "repin" it.  Right now I can browse, but you have to sign up to use all the functions and to sign up you need to be invited AND apparently there is a waiting list to sign up.  I don't know why there is a limit on members.  That seems sort of counterproductive to business, but I don't pretend to understand the business of Internet sights anyway.  Try it out and see what you think.  As always, if anyone has any comments, good or bad about it or can shed some light on the workings of the whole thing, please share!