You're obviously aiming for a more design-focused crowd, but why I've stuck to pinboard.in for so long is because I don't want the primary display of my bookmarks to be a gallery of thumbnails. I'm usually bookmarking interesting articles or essays and the best way for me to sort through those is a good use of tag filters and search...anything else, including images, is just noise.

However, that's different if what you're doing is bookmarking visual elements. But if that's the case, it's hard to be Pinterest.