I worked with XSLT a few companies ago. They had several XSLT documents as a transformation to various output formats (this was a pretty minor part of the overall product).
I'm not sure I've ever seen something less popular. Feature requests and the odd bug would build up, eventually an engineer would be assigned to it for a week and they'd fix a bunch of things, then essentially would rather quit than keep doing it, so next time it'd be someone else's turn.
I don't even think it was particularly bad. It seemed like it was just always like that. Thank goodness it isn't so popular any more so it doesn't turn up jammed into random places as it did then.