There have been a bunch of times where I've asked it to write me a snippet of code, and it cheerfully gave me back something that doesn't work for one reason or another. Hallucinated methods are common. Then I ask it to check its code, and it'll find the error and give me back code with a different error. I'll repeat the process a few times before it eventually gets back to code that resembles its first attempt. Then I'll give up and write it myself.
As an example of a task that it failed to do: I asked it to write me an example Python function that runs a subprocess, prints its stdout transparently (so that I can use it for running interactive applications), but also records the process's stdout so that I can use it later. I wanted something that used non-blocking I/O methods, so that I didn't have to explicitly poll every N milliseconds or something.