Eric Garrido on feed formats: "Here’s the bottom line: Stop advertising the older formats. It’s fine to continue to serve up the others, just don’t actively advertise it. No one cares what formats you advertise, or the format they click on, as long as they get the content they want."
I said something similar @Blogtalk 2008 during the microformats and mashups panel discussion - beforehand there was a presentation by Anna Rogozinska on a dieting website. The site was entirely focused on dieting - except for one thing - the pages advertised 3 or so different feed formats. It was like seeing a tear in the Matrix.
For people like me who are building systems and defining specifications, which one to use is important. But for the end user, it's just data; the details of the particular format aren't that interesting.