David Carlisle is currently undertaking a project to convert XQuery expressions into other languages, by first converting the query to XML and then on from there.
The "xq2xml" page can be found at http://monet.nag.co.uk/xq2xml/index.html
His notes on the differences between XQuery and XSLT can be found at http://monet.nag.co.uk/xq2xml/xq2xslnotes.html
It's all very interesting reading, but I kept asking myself "why?" so I mailed him asking if there's a real world application behind all this...
David's reply: "is 'teach myself xquery' a real world application?"
I guess the "because it's there" mentality applies to programming too :)