Sounds radical, but I would say Google PR is dead. And long live the UE(user experience), if Google is capable enough to discrete it at all.
Because of PR, so many people are crazy about link building. Those madness produced lot of link farms and useless sites and blogs just for links, and the rampant spamming partially because of it.
Link is only useful when visitors to that web site have a big possibility to find useful stuff though visiting lined sites. Otherwise, it do not make any sense at all.
However, as far as I know, Google PR does not smart enough to rule out useless links. That is the reason that so many people drove into Google PR rush, rather than think about what users really like.
Ad rules of thumb, pay more attention to your visitors. Providing useful info, fresh content, and clean, semantically sound HTML, css, and js. I am sure you will be fine eventually.
By the way, Google made a statement months ago that they will abandon PR, for ever. Hurray!