First of all, implementors of anything Atom-related need to spend some time chez Jacques Distler; in particular, the conversation that plays out in the comments. Second, there’s this piece of software called Planet Planet that allows you to make an aggregate web page by reading lots of feeds; for example, see Planet Apache or Planet Sun. Sam Ruby decided that its Atom support needed some work, so he did it. Now, here’s the exciting part: he pinged me over the weekend and said “Hey, look at this” wanting to show me his cleverly-Atomized Planet Intertwingly feed. I looked at it in NetNewsWire and was puzzled for a moment; some but not all of the things in the feed were highlighted as unread, even though this was the first time I’d seen it. Then the light went on. This is Atom doing exactly what we went to all that trouble to make it do. NetNewsWire has good Atom support and, because Atom entries all have unique IDs and timestamps, it can tell that it’s seen lots of those entries before in other feeds that I subscribe to. That’s how I found Jacques’ piece. This is huge; anyone who uses synthetic or aggregated feeds knows that dupes are a big problem, showing up all over the place. No longer, Atom makes that problem go away.