Imagine you have users that want to view an XML document as a report of some kind. You can easily do this right now by having them upload a document and attaching a stylesheet to it. I do this to let people view after-game reports for a video game (Nebulous: Fleet Command). They come in as XML and I transform them to HTML. Now I do this all client-side using the browser support for XSLT and about 10 lines of javascript because I don't want to pay for and run a server for file uploads. But if I did the XSLT support in the browser would make it truly trivial to do.

Now this obviously isn't critical infrastructure, but it sucks getting stepped on and I'm getting stepped on by the removal of XSLT.