Used XSLT for the first time at work. It seems like it can be a pretty powerful tool in the right situation, but I'm not too happy that I have to use it in the first place.

We use it for creating custom reports of a large set of data... And people keep complaining they can't get the report they want. If only there was a way to customize the output to your liking...

I had to write an entire format conversion utility for a project, and used it to write the conversion. It's an interesting language...it's almost fun tail, but not quite. Turned out to be pretty useful in my case.

One trick I learned: If it doesn't offer the functionality you want, you can write the functionality in the host language (mine was C#) and expose it to the XSLT engine. I had to write a bunch of bitwise parsers and math functions to do my conversions, and there was no way I was going to use recursion and try to implement them in XSLT haha.