Client side XSLT has one terrific advantage : it allows splitting up a page into dynamic and static parts. This allows you to cache almost-static-but-not-really pages very efficiently. E.g. a news paper front page with a “logged in as…” section top right, but otherwise equal content. Or HN comment pages for logged in users, which currently are uncached and can cause quite heavy load on the server for heavy threads, simply by virtue of people viewing it. I remember a situation where they explicitly asked: please log out when viewing this comment page—that shouldn’t be necessary.

I still think client side XSLT is a good thing. I write simple documents and it is automatically converted client side. The world's best static site generator.

I gives me the best of two worlds: simple markup with complete control of output and CSS styling and instant changes of all documents without a compilation step.

XSLT got an unfair shake. Yes, XML is ugly, and verbose, and painful to write code in, but the ideas were very good. Most users never understood the processing model or the declarative/functional nature of XSLT, and so tried to write procedural code with it, with predictably nasty outcomes (hint: <xsl:if> is almost always a code smell). But those who did get it, could use it to write some pretty elegant little programs.

I liked XSLT for XML to XML but using it for creating HTML was a nightmare.