Just discovered: if i click the little arrow that appears at bottom of any post on Andy's River, it leads me (after i approve connection with my Twitter account) to another river where i can post to Twitter, with some added value beyond the standard 140 character text box, in form of Title, Link and Enclosure. Dunno what's going on here, but hey: it's cool, so i'll take it, no questions asked!
That's River3, another blogging tool from Dave Winer, the one I use for most of my posting to Twitter. It generates a listing in chronological order of all postings generated with Radio3 (a linkblog with an RSS feed) with a blue Twitter bird button to click on to view any individual tweet. It's a very handy tool and the integration with the river of news makes it even better.