Something I've been working on at work deals with feeds - I have to read, parse and derive meaning out of RSS and Atom feeds in the wild.
And it's not been fun.
The Universal Feed Parser is nice and everything but I'm still being forced to debug through weird Unicode issues. Or issues like some Feedburner feeds having the original permalink in feedburner:origLink
Well, atleast I'm not the only one facing these issues. Sam Ruby maintains a list here and the Google Reader team talks of the problems they've run into (and I've run into a lot of them as well)
[Cross posted at my new blog at http://www.sriramkrishnan.com/blog/2006/07/feed-mess.html. Post comments over there. Subscribe if you feel like it too :-)]