Jon Udell's column in this week's InfoWorld is about XML's quirky namespaces. Jon points out that recent moves by Microsoft and Apple have brought namespaces to the fore and people will have to deal with them sooner or later.
I'll second Jon's statement that namespaces can be a pain. As he says, every tool seems to treat them differently. And not in a trivial way--tool author frequently have deep-seated philosophies about how namespace should work and build that into the tool. Just when you think you know what's what, you start up another tool and are forced to revisit the underlying philosophy of namespaces to understand how to tame it.
In my most recent project, I've mostly punted on namespaces, recognizing that that was a big bit of "programming debt" I'd have to pay off later. I'm to the point now where it needs to be tackled and I'm not looking forward to it.
Jon recommends Ronald Bourret's Namespace Myths Exploded as a good bit of reading. I just reread it and agree that it's full of useful information. It's not likely to answer many of the questions that programmers will face as they struggle to use namespaces in their XML. Those will continue to revolve around tools and the quirky ways that they differ. Hopefully we'll get all this worked out as we use namespaces more and come to some collective philosophy about what namespaces are and how they can be used. Until then, plan on some late nights.