Brad released a prototype for Atom Stream server for LiveJournal today, Ben was working on TypePad to support the upstream push from TypePad weblogs. Hence I spent a couple of minutes to write a consumer library: XML::Atom::Stream. It uses SAX based XML parser (XML::SAX::ParserFactory) and splices the stream into individual <atom:feed/>s, with which you can do whatever you want.
We chatted about the idea of Atom stream in the last weekend. That's pretty quick and I love it. And yeah, this is part of our first-step answer for weblog Updates ping and RSS Ping stuff. See also Ben's Post with nice background information about pings.