PR is Google’s way of grading pages for its search tool. It uses linking as a vote system. Quality blogs connected to other quality blogs are highly relevant. And links to relevant, quality blogs get a higher page rank.
And what would a higher page rank mean? Well, for those those who monetize (or try to) their blogs, a higher page rank means that your blog will be easily marketable to advertisers.
Read Darren’s blog for the nitty gritty on how PR is computed. Or, go check out what Google Data Center is saying about your blog’s page rank…