I'll add another comment in the hopes of keeping this idea alive. It's the lack of this feature that keeps me on LJ, and I was reminded of this when LJ needed a reauthorization to access my Twitter. I'm hoping that whatever allows LJ to get around the Twitter TOS on importing content can apply to DW as well, as I would so like to see this feature implemented.
I don't need the hashtag idea though could live with it if implemented, and I only need public tweets for my uses--like others, it's my archive of tweets plus makes them accessible for a few friends who don't use twitter.