Depends on the school. For example, HBS has over the years whittled down the rec letters -- this year, it's just three questions with a 250-word limit for each question. They've only introduced word limits in the past few years (as have some other schools), which is a HUGE hint to keep it concise. They aren't going to wade through mountains of text.
Put yourself in their shoes. Each adcom looks over a couple hundred applications over a few months. They spend maybe 15-20 minutes on each application. If you were them, would you bother to take a close read when you see a rec letter that is chock full of really long text?
Alex Chu
alex@mbaapply.com
www.mbaapply.com
http://mbaapply.blogspot.com