Google and atom.xml
Dave Winer noted that Google seems to be looking for atom.xml and not looking for RSS. I can offer a data point that seems to support that.
A few days ago, Zim opened a new website with a mobile weblog application so I've had an opportunity to watch the referers and links to the site slowly spreading.
Our very first hit from GoogleBot was on /robots.txt (a 404, we don't have one yet), the next was on /Default.aspx. That was the first visit.
The next GoogleBot visit was an hour later when it requested /robots.txt (still a 404), and then requested /atom.xml.
We don't support Atom, although we do support RSS.
Why might Google poll for atom.xml? Well, it's got a fairly standard name as opposed to RSS, so that might be one reason. Conspiracy theorists can speculate that maybe it's the one thing that would get sites to support Atom in addition to RSS, since every reader that can read Atom also supports RSS (so there's really no compelling reason to support Atom if you're a web developer)...