Answer to your first question : “PageRank is [only] one of the methods Google uses to determine a page’s relevance or importance.†Google uses many factors in ranking. Of these, the PageRank algorithm might be the best known. PageRank evaluates two things: how many links there are to a web page from other pages, and the quality of the linking sites. With PageRank, five or six high-quality links from websites such as www.cnn.com and www.nytimes.com would be valued much more highly than twice as many links from less reputable or established sites. PageRank has only ever been an approximation of the quality of a web page and has never had anything to do with the measuring of the topical relevance of a web page. Topical relevance is measured with link context and on-page factors such as keyword density, title tag, and everything else.
Some important impacts on pagerank : 1. Frequent content updates don’t improve Page Rank automatically. Content is not part of the PR calculation. 2. High Page Rank doesn’t mean high search ranking. 3. DMOZ and Yahoo! Listings don’t improve Page Rank automatically. 4. .edu and .gov-sites don’t improve Page Rank automatically. 5. Sub-directories don’t necessarily have a lower Page Rank than root-directories. 6. Wikipedia links don’t improve PageRank automatically (but pages which extract information from Wikipedia might improve PageRank). 7. Links marked with nofollow-attribute don’t contribute to Google PageRank. 8. Efficient internal onsite linking has an impact on PageRank. 9. Related high ranked web-sites count stronger. But: “a page with high PageRank may actually pass you less if it has more links, because it’s spread too thin.†10. Links from and to high quality related sites have an impact on Page Rank. 11. Multiple votes to one link from the same page cost as much as a single vote. Enjoy !!!