Interesting thread over at IMR...
To sum it up, it seems (I could be wrong) like Google is not allowing phpbb.com (which is a PR10 site) to pass along Page Rank. I have not found a single link that any page within phpbb.com links to that is reported as a back link for that site (with the link: function). In case anyone is wondering, there is no blocking via robots.txt (I even went so far as to spoof my user agent to look like googlebot to see if they are cloaking anything... which they aren't).
