Well I'm a writer of excessively long content... including a twenty thousand word review of The Social Network.

http://reviewsindepth.com/2010/11/the-social-network-the-end...

It makes an interesting test case of what people are willing to put up with length wise in a blog post.

In this case the post has been visited 11763 times by 10880 uniques. The average time on page is 8 minutes and 3 seconds. Certainly not long enough to read the entire article - but it's a fairly significant degree of engagement.

Different sources yield differing amounts of engagement. Avg time on page for (min:sec)

Facebook: 23:41 Google: 13.37 Hacker News: 12.42 Twitter: 9:00 Reddit: 6:12 givementsomethingtoread.com: 5:18 instapaper: 4:47 tumblr: 2:32 stumbleupon: 0:06