Google only scores the first 500-something words on a page (I can't remember the exact number). So, assuming you follow newspaper etiquette (teaser, body, summary), your pages should be "naturally" optimized because Google wants, hey, real content.
If you absolutely need to post something long, either A) break it up into logical sections and create & title separate pages, or B) use a "Read More about <topic>" link to keep the SEO juice high.
You can't have too big of a site, but excessively long pages don't help anyone.
-MattL
PS- average page view is 12 seconds, average content page view is 26 seconds