Just because the Internet provides you with a seemingly endless amount of space, doesn't mean you have to cram every last inch with words. It's not a clown car people.
If you're going to write a really long blog, the content better be really, really good, or readers are going to X out of your web page faster than you can say "click."
Besides, good content can come in miniature size too. Take Seth Godin's Blog, for example. Short and sweet; Effective and powerful.