Almost certain this doesn't qualify as "nice", but: Namespaces make XSLT more powerful than one might think at first, because they allow you to write XSLT that generates XSLT (and so on...) by switching a namespace to a different one upon output generation.

Of course, the result is often barely readable anymore, so there's that.

Edit: On the other hand, the difference between XSLT-namespaced elements and all the others in a stylesheet is the one thing that makes basic XSLT readable, since you don't have to use a full meta-language just to create simple elements.