It addresses the point of people being afraid to express themselves because there is almost always a large mass of objects to pin - so you should feel more comfortable pinning something that you may or may not be secure about your friend's agreeing with. If someone was to think "Wow, those shoes are ugly" and you had it pinned - hey, it's a huge pinboard and I'm sure they agree with more things about you than they disagree.
It's also a complete positive board - much like the like system is, there isn't a way to track how many people don't like something - so there's safety in numbers of pinning something someone else already has pinned.
I think that something innovative that could possibly be added towards the pinning system is to allow people to add their own tags to the objects that you can pin - and allow people to add the pins to their own groups - and allow these groups to be reviewed publicly like a portfolio. It would be much easier to obtain information about people who like groups of specific objects then. (Assuming this isn't already done - I'm not a Pinterest user myself.)