Jotsy is a very slick document annotator that RIM showed off during the keynote at BlackBerry DevCon Americas a few months ago. It was scheduled to ship with OS 2.0 and is now coming out in a public beta on App World. The app is built on HTML5 and allows you to annotate documents from the PlayBook with their cool interface. You can then synchronize those documents and annotations with your PC. You need the PC app for that which you can find at www.jotsy.com.
You can check out the Jotsy beta in App World free. The premium versions are planned to be coming in Q1 2012 so there should be a few updates by then!