My biggest problem with ChatGPT, in playing around with it a little and admittedly trying to get it to break, is that it seems to have a really difficult time saying "I don't know", particularly when confronted with non-standard questions, and will proceed to bullshit something instead. (Not entirely unlike some humans, but still.)
As an example, I asked ChatGPT what the lyrics were to "Jessica" by The Allman Brothers Band. This tune actually is an instrumental, so the correct answer is "there are no lyrics". However, ChatGPT proceeded to give me this nice bit of... something. (https://imgur.com/T3nGv4L)
In another example, seeing what ChatGPT made of the infamous "bananadine" hoax of the 1960s, I asked ChatGPT what drugs could be made with banana peels. After correctly asserting that banana peels don't contain psychoactive substances, ChatGPT proceeded to mention that "there are some reports that banana peels can be used to make a hallucinogenic drug called DMT". (https://imgur.com/a/9fvhQJh) Huh.
Another trick question I tried: "Who won the 1980 USAC Indycar race at Talladega?" This refers to an obscure cancelled race during the 1979-1980 CART/USAC split, which I doubt most people would be aware of unless they are very into American open-wheel motorsport. (See this video: https://www.youtube.com/watch?v=K433p727f-0 for the story if you are interested in the details). So generally speaking, I would expect the general reaction among most people to be "I don't know". ChatGPT instead decided to answer, with confidence, that Johnny Rutherford was the winner of this non-existent race. (https://imgur.com/a/J2KJoGN)
So, it's a little bit more than not knowing the facts about the world, it's the bullshitting an answer thing that I see as the biggest problem. It's admittedly impressive when it comes up with correct answers, but until the "confidentially incorrect" side of ChatGPT disappears, it is not a reliable source (not that OpenAI ever claimed it as such, but I wouldn't trust ChatGPT to 100% "do my homework" for me at this point like some stories suggest it could.)