Yes, I use it regularly to log my working hours since ~2 months. However, initially I started with a different format which was basically just a YAML schema. That worked well for processing the data, but it turned out to be too verbose to type by hand. A big inspiration came from ledger (an accounting tool/format), which I appreciate a lot because it’s very powerful yet it has a dead simple syntax.

I too think that plain text is very underrated. I think though that this is more due to the tooling aspect than to the data format itself. (Especially if there is only a CLI application.) I like the note management tool Zettlr for that matter, because it demonstrates how both things can be combined.