I tried vibe coding with Copilot Agent mode the other day just for fun. I needed a small web UI (two forms, a handful of buttons, single page, no backend) for a hobby project. The UI was just for a non-critical part of the project. It won't see a lot of modifications, it was made from scratch, so basically the perfect circumstances for easy coding.

I'm a backend/embedded developer and while I can find my way around FE code, I don't know anything about which framework is currently hype and I didn't really want to get into learning all that for just a very simple little hobby tool.

Vibe coding kinda mostly worked.

It did create the app I wanted with comparatively small amounts of manual coding.
It did help with my lack of framework knowledge

But that's where the positives end.

It made mistakes all the time resulting in syntax errors, which it reckognized itself and asked if it should fix them, and when I said it should, it just made many, many more syntax errors. So at that point I had to stop using it, fix the errors manually and only then return to vibe coding.
One issue I had all the time was that it would put correct lines in the wrong locations. For example, a change should add a line to a list (among other things). It did generate the correct line but put it 100 lines later right in the middle of some function code.
The most annoying instances of that were that it insisted on putting each new function on line 1 before the import statements and outside of all components.
The produced code was horrible. Like, comically bad. All in one 1500k lines file, duplicate and dead code everywhere, no clear code standard, every function looks like it was stolen from a different project.
It implemented a few things that I didn't ask it for, and when I asked it to remove it, it only removed the feature from the DOM, leaving all supporting functions and variables intact (thus producing dead code).
I had to do some manual touch-ups for things it couldn't do, and it was really difficult to do sue thanks to the spaghetti-origins of the code.

If this was a real product that was to be maintained for a longer period of time this would be horrendous to maintain.