Yaron Goland has published a thought-provoking entry about Atom. It's fun to read too.
I've never seen Star Wars before, not a single episode, I should've. I didn't immediately recognized
who a General Weasdel was, and only after reading an interesting discussion on a Sam Ruby's blog did I realize who Darth Sudsy was :-).
In short, one of the questions Yaron raises is : when to use documents in the Atom syndication format (ASF) given that one has to tunnel custom XML inside individual atom entires as opposed to just passing this given XML around as is ?
Whether the example Yaron uses is contrived or not, it's hard not to notice, that yes, one just adds some extra layer of complexity when wrapping the content inside Atom entries. Yes, the example shown can be reformatted to make it more readable, but one still will have some markup there which has nothing to do with the original content.
So when is it worth it ? I've tried to contemplate a bit about it here and I'm glad to see this discussion happening now.
As far as I'm concerned, figuring out when to use ASF is the least difficult part. Dare Obasanjo points to the fact that Atom is good at representing the streams of (timestamped) microcontent and Sam Ruby and Yaron offer some thoughts on when Atom is better be used. This comment also suggests that Atom-wrapping a given content is not a de-facto choice, it depends on what people want to achieve by doing so.
I see ASF be particularly good at representing arbitraty types of events, for example.
The difficult question is when is it really worth using Atom Pub as an application level protocol of choice ? Just because there're Atom-enabled client tools out there ? So far I feel it matters only when the generic tools are targeted, but I may be wrong.
Another reason which is cited often enough is that Google does is, with its GData protocol. Oh, man, Darth Goo-Goo-L and his general G'Day tah, :-), that is. The idea of a wide-spread internet programming with the help of GData-enabled client libraries might not be that far-fetched at all, you never know :-).
And I thought it's all just about sending simple XML around :-). The battle is just beginning, which format to use and what protocol to use, and so on and so forth :-)