Geek Boards is currently a PR5 which is quite decent. There are a lot of outbound links in the site which may be preventing it reaching the peak.
In answer to the PageRank question. PageRank is the brain child of Larry Page who inveted Google. He came up with a way of scoring websites out of 10 based on a number of factors (currently at least 250-300). A site with high PageRank (PR) is more reputable and is likely to be positioned higher under relevant searches.
