My most successful use of AI so far was that Bard's answer was so useless that it made me realize the actual problem. Invoking Cunningham's Law isn't really a success on its own merit though.
What was the question and what did it answer? For me as a startup founder, it's cutting down my coding time to 1/4 of what it would have been, since I can ask ChatGPT clarifying questions and ask it for direct code examples.