Most website design book keep reminding designers that content is the main thing, and that the design should serve the content and not the other way around.
I think that most people that make a website have content and trying to find a space to display it - weather they make art and want to sell it, or have a product they seek to promote or just want to share family pictures or a hobby.
So I think it really depend on your site and what you are trying to get by getting one going. You can produce content yourself by writing and taking pictures and making drawings or animations. It's possible to hire proessionals copy writers \ illustrators \ animators \ photographer to manufacture content for you, or, you can also go web0.2 and appeal to the public to manufacture content like in Yedda, flickr or blog sites.
