It seems that posts with 1000+ words rank better, because they allow for more long tail keywords to naturally occur. I can validate that in a niche I am going for, top rankers have long posts.
However, the people above who said that lots of people don't have that kind of attention span are right. If you plan to write a long blog post, makes use of bullet points as well as big headers to break up the text and make it more likely for them to read it.
Part of it depends on the type of post. If it is a post designed to be informative it can be good to make it high quality, lengthy content.