I don't think so (at least, not in my sector): for Key Term none of the top ten results are above PR3 (the #2 spot is PR1!), and running backlink checks on them shows a backlink profile consistent with their PR value.
Wilb, how did those results change due to this Penguin update though? I mean, if the PR1 site was top but is now second and has been replaced by a site with a stronger link profile, that says one thing. But if the PR1 site came straight into the top 10 in second position yesterday above lots of sites with stronger backlinks, that says something else.