Everytime I use XSLT, it leaves a really bad taste in my mind.  I just spent 3 hours writing an XSLT stylesheet for a new XML-based signature verification result format I created for my client recently.

The format itself is designed to capture data associated with signature verification so that it can be used as legal proof of verification at some later date.  This means capturing data hash, signature, certificates, and OCSP request/response pairs for each cert in the chain; basically bagging every scrap of data on the table.  End result should be routed automatically to a backend repository, but some customers will opt to stored them on local drives which means they need to view it locally.

That's where XSLT comes in.  By associating an XSLT stylesheet with the XML file, users can view the file with just a browser (well, IE).  It's a nice solution except writing XSLT can be a real pain in the ass.  Take one little step outside the simple stuff and you are in a jungle and it doesn't get better over time unless you use it everyday.  Since what I had to do involves fairly advanced XSLT, I was not in a good mood by the time I finished.

If you have a choice, avoid XSLT like the flu.  I didn't.  If you really have to, make sure you have a XSLT debugger.  XSLT being a declarative language is a joke.  It might look declarative, but if you do any serious work with it, you will start thinking procedurally in order to make sense of it.  Like I said, it's a joke.