@cstross It is useful for figuring out syntax of fairly popular languages that you are just learning or don't use often. It is not useful for writing code.
E.g., I have had good luck asking about basic Rust questions, including debugging and explaining my borrow-checker-fights; help writing basic RegEx (since I can never ever remember anything RegEx).
If I were learning TS or JS or SQL I'm sure it would be helpful. It can probably help write a tricky TS type for example, but I don't really need help with those things.
I found it quite bad at languages with less StackOverflow coverage, like Elixir. And forget about, say, the 2023 version of Elixir LiveView - the AI can't help you there.
Also once you get deeper than the basics, it doesn't keep up with the times very well. So one thing I haven't heard much is how it would like to create a tendency towards stagnation in the ecosystem.
By "it" I mean the GPT versions, 3.5 and 4.0. The Google ones are still only good at feeding you rocks.