Do you think generative AI like ChatGPT is useful for content marketing? Can it replace a content writer altogether?

Usefulness of ChatGPT depends on which industry you would like to use it for.
Some industries and businesses must carry a high level of authenticity, originality and creativity, none of which ChatGPT is able to provide. These industries include fashion, publishing, art, to name a few.
However, it can be more useful in the industries where content needs to be factual, without any "fluff". 
Nevertheless,I would not replace content writer with AI tools given that we are in the early steps of NLP development.

I find ChatGPT extremely useful for generating short-form copy, especially for social media and content ideas. While it can enhance creativity and streamline certain aspects of content marketing, I don't believe it can replace a skilled content writer, particularly for longer articles or in-depth pieces. For substantial content, I collaborate with an experienced writer, leveraging their understanding of the business world and ability to ask the right questions to develop compelling articles. The rise of generative AI is prompting B2B marketers to be more innovative in their content writing, although it's crucial to maintain authenticity to distinguish between AI-generated and human-crafted content, especially on platforms like LinkedIn.

Generative AI like ChatGPT is undoubtedly useful for content marketing, offering valuable insights and a head start for writers. However, I don't believe it can entirely replace content writers. While it saves time and provides general content, the lack of personalization and generality might limit its effectiveness. Factors like data accuracy, security concerns, and the diversity of software options all contribute to the continued necessity of human content writers in the industry.

I think it's great for research and brainstorming ideas, once we get to the actually writing aspect though, best left for humans

Chat GPT4 (the paid offering) is much better than the free 3.5 version regarding accuracy and output, so I would recommend the upgrade for any testing.  The new capability to add your corporate tone of voice information to the custom instructions area is very helpful in getting the content on point faster.  Proper prompting is very important as well - it is incredible what you can generate with practice (tables with variable content).  Remember that you can tell ChatGPT to write as if it is a certain person (write this as if you were a product manager, etc.).  

I found it invaluable for taking transcripts from webinars, or whitepaper content and repurposing it into blog posts and SEO articles - and then deriving shorter form content, like social posts, from those.