I think the goal of tumblr for me is less sharing, more curating

That makes sense-- and for tumblr, you do have pretty excellent taste. But for me, it kind of crosses the line between watching some awesome cat video on YouTube and MAYBE sending it to my husband via IM or spamming that same video to my entire address book. I have my little picture hoards and bookmark hoards and such and I guess it'd be nice to have them all in one place with tags, so I can see the appeal there.

But in terms of interaction with other people/entities? Deeply dissatisfying experience.