I guess there is some relationship - bounce rate is also one among the factor to calculate
PR - it may be I am not sure about it..
In my site, one of my inner-page got
PR 0 for which I never did SEO, but it got
PR because of click-through rate - I got 100-200visits/month for that page itself because of nice content.. (for some reasons, I am not able to give the link for that page)
So, I thing user-friendliness is also calculated for calculating
PR - I guess bounce rate may be one among the factor..