According to Jeremy Zawodney the “My Yahoo's RSS module also groks Atom. It was added last night. It took about a half hour.” Seeing that he said it took only 30 minutes to implement this and there are a couple of things about ATOM that require a little thinking about it even if all you are interested in is titles and dates as My Yahoo! is I decided to give it a try and subscribe to Mark Pilgrim's Atom feed and this is what I ended up being shown in My Yahoo!
The first minor issue is that the posts aren't sorted chronologically but that isn't particularly interesting. What is interesting is if you go to the article entitled The myth of RSS compatibility its publication date is said to be “Wednesday, February 4, 2004” which is about a week ago and if you go to the post entitled Universal Feed Parser 3.0 beta its publication date is said to be Wednesday, February 1, 2004 which is almost 2 weeks ago not a day ago like Yahoo! claims.
The simple answer to the confusion can be gleaned from Mark's ATOM feed, that particular entry has a <modified> date of 2004-02-11T16:17:08Z, an <issued> date of 2004-02-01T18:38:15-05:00 and a <created> date of 2004-02-01T23:38:15Z. My Yahoo! is choosing to key the freshness of article of its modified date even though when one gets to the actual content it seems much older.
It is quite interesting to see how just one concept [how old is this article?] can lead to some confusion between the end user of a news aggregator and the content publisher. I also suspect that My Yahoo! could be similarly confused by the various issues with escaping content in Atom when processing titles but since I don't have access to a web server I can't test some of my theories.
I tend to wonder whether the various content producers creating Atom feeds will ditch their feeds for Atom 0.4, Atom 0.5 up until it becomes a final IETF spec or whether they'll keep parallel versions of these feeds so Atom 0.3 continues to live in perpetuity.
It's amazing how geeks can turn the simplest things into such a mess. I'm definitely going to sit it out until the IETF Atom 1.0 syndication format spec before spending any time working on this for RSS Bandit.