For how important a PageRank is...I would say, it's only as important as Google is. Or, more specifically, it's only as important as Google is to your website! Google ranks websites based on a scale from 0 to 10, measuring the "importance" of websites. If the bulk of your web traffic comes from Google, and your Page Rank drops, you're in trouble. But high PR means more traffic coming to your site through Google search.