Hi Jan,
I would imagine the Pinterest links are all "nofollow" and not passing authority, also the link from Polyvore is also "nofollow".
The reality is there pages have more authority, the title is the same and at present that is why you are being outranked.
I guess the most important question is; "does it matter very much?" - I haven't searched the keyword tool for an estimation on search traffic, but I'd hazard a guess it is slim to nil. The fact that they outrank you due to SEO factors is unimportant if there is no organic traffic. You outrank them on the social factors, hence the larger following and that is where the traffic is, so if I could pick more Pinterest traffic or more Google traffic for this instance, I know where I'd be putting my money.
Hope this is of some assistance.
