In a cynical way... you are on to something. Let me know early on if you ever plan on selling an ebook ! Hence, I can make good money before it gets totally splashed everywhere and before Google feels that it needs to redress the balance.
I agree with Steve, PR is even less than it was 2 years ago... Its still there for sure. Sites went nuts on backlinks from anywhere just to compensate on mass against high PR sites. I know of examples where that actually worked to the annoyance of one of my clients back in 2008.