Size Doesn't Matter
If you have ever wondered how long is too long ... and of course I'm talking about a piece of writing, what were you thinking?? ... then you should read this post from Copyblogger.
The "shorter is better" mantra seems to pervade throughout internet content, but the point that Copyblogger makes is that it's not the size of the blog post that matters, it's how well the story is told. (I know, I know ... the dirty analogy just writes itself.)
In general, I agree with this. A long but well-written and cogent post is far more interesting than a short but dull post.
But I do think that writers need to consider if they have the right medium for their message. While long blog posts are not inherently bad, you might consider whether what you really need to do is write a whitepaper.
Formatting counts, too. Lists (both bulleted and numbered) can help carry the reader through and allow easy skimming. And while it will horrify your English teacher -- who probably taught you the 5-sentence per paragraph rule -- shorter paragraphs are easier to read online.
So the takeaway here is simple: focus on your story! Tell a great story and size really (really!) doesn't matter ...