Doing content marketing right, means writing a couple assignments per week, and a thesis or two per month. And you get graded constantly by your users.
The idea of Inbound Marketing is not that new, people have been doing it with Content Marketing. The problem is though, that it's really hard to convince people what good content means. It doesn't mean selling your product, it means educating the user. And this is where, I think, a lot of companies, and a lot of "marketers", at least in the beginning, get it wrong. It takes a lot of effort to produce good content, and in a startup or a small company, people often fail to understand that. The ability to write fast, does not mean you are capable of producing quality content fast - that takes time, and research. So don't think of time spent on blog posts, e-books and whitepapers as wasted time, think of it as an investment. Measure it, and you'll see the results. Not immediately, but through time, the users will start coming and the leads increasing.
What is valuable content? It's not promotional material. Out of the companies I'm following lately at my position at Zeppelin, one that really stands out in my opinion is Help Scout. The list of resources on their blog is awesome, and it is all around how to improve your customer relationship/support processes. It is perfectly relatable to their product, but it's showing the product off through valuable content, not the other way around. Another example is the company that more or less redefined Inbound Marketing - Hubspot. Unsurprisingly, the content they produce every day is really high, because that is basically how they make their living - selling inbound marketing. Granted, for me personally, that's too much content. Studies have shown that there is an optimum number of posts per week that resonates, and I can see how they can afford to produce that number. At the same time, for a startup, there is no way imaginable to produce that much. But still, if you're looking for a good example, check them out.