For me, I think of the reblogging "cool" stuff as more self-reference, I guess. I have tags on my own blog that I go to when I want to look at cute stuff to cheer myself up, or awesome art to inspire myself. That kind of thing. I think the goal of tumblr for me is less sharing, more curating -- with a side of the "too frivolous for my serious journal" stuff. But it's definitely not for everyone, and I think if I didn't have a lot of friends who used tumblr exclusively, I wouldn't still be there.