Dare Obasanjo just filed some notes from Gnomedex - I spotted this exchange between Bob Wyman (of PubSub) and an audience member:

A member of the audience responded that he used multiple formats because different aggregators support some formats better than others. Bob Wyman replied that bugs in aggregators should result in putting pressure on RSS aggregator developers to fix them instead of causing confusion to end users by spitting multiple versions of the same feed. Bob then advocated using picking Atom since a lot of lessons had been learned via the IETF process to improve the format. Another audience member mentioned that 95% of his syndication traffic was for his RSS feed not his Atom feed so he knows which format is winning in the market place.

That's about the size of it. Google is pushing Atom via Blogger, but outside of that, it's mostly RSS. You can whine, argue, fuss (whatever) - but that's the reality. In the end though, it doesn't matter that much to end users - most aggregators support all the formats (I certainly do in BottomFeeder), so we are going to end up in a place where users will subscribe, neither knowing nor caring what format they get.