The latest update of Google's pagerank gives most of my problem sites pagerank 3. But they have very poor ranking in the search result. why?
Your rankings have nothing to do with your PR you can even have a PR 6 but still have a chance of not ranking anywhere near the top 10. PR depends upon the number of links a particular page has but rankings are far more complex than that. First of all in-order to rank well you have to do a keyword research and find a keyword that describes your niche and doesn't have a very tough competition. After your keyword research is done then only you can think about the other things. If getting higher rankings is your target then start learning SEO. Read this for a starter - http://www.google.com/webmasters/docs/search-engine-optimization-starter-guide.pdf and also http://searchengineland.com/guide/what-is-seo
Well, in order to rank, you need more quality back links, and better content. Without those two, your site won't ever have good rankings.
Google seems to pay more attention to the content in the site and penalizes those sites that use spun articles to build backlinks.
One quality back link is better than 10 ordinary back links. Quality back links could come from top authority blogs and quality contents. Page ranking takes time, and a whole lot of work. Choosing the keywords is also essential.