Been hearing about WASM on here for years now, but it's never about people actually using it. Are there any high-profile cases of it being used?

One that comes to mind is the WASM port of FFmpeg:

https://github.com/ffmpegwasm/ffmpeg.wasm

Another is the SQLite WASM project:

https://sqlite.org/wasm/doc/trunk/index.md

Also v86 for x86 machine virtualization in the web browser:

https://github.com/copy/v86

A fun project is WASM-4, for building retro-style games:

https://wasm4.org/

Possibly more interesting projects to be found here:

https://github.com/topics/wasm

https://github.com/mbasso/awesome-wasm