I have websites that rank #1 with PR0, PR1, and PR2, and websites that are PR5 and PR6 that don't even rank on the first page. A couple of the low PR sites target smaller niches, and the high PR sites target more popular keywords, but sometimes the other way around.
I use everything from varying keyword anchors on backlinks, keyword-targeted domain names, deep linking, linkbaiting, signature links, directory submissions, link exchanges, topsites, cross-linking, and several other strategies I don't even think have names yet.
