Those who watch their PageRank closely may be interested in this purely speculative concept from the fine folks at SEORoundtable - fractional PageRank.
The concept emerged from this question - how does Google decide how to rank pages with the same PR? Though there could well be other factors involved, one hypothesis (only a hypothesis), from relaxzoolander of SEOChat, is that there are PR fractions that help Google decide which page should show up on top.
So if your site is PR5 how can you tell if it's a low PR or a high PR?
Digitalpoint, SEOChat poster (and creator of the Channel Data Charting AdSense Tool), postulated, "let's say you have a PR7 site, and normally everything one-click deep is PR6, well if you have a 'high' PR7, everything one-click in will also be PR7."
As rustybrick put it, "if your pagerank is currently a 6 and your main four inner pages are a pagerank of 5 then it is safe to bet that your homepage's PR 6 is a low PR 6."
Everyone involved in this discussion was careful to point out that their thoughts are purely hypothetical and that there are many many factors involved. I'll leave you with relaxzoolander's caveat to speculators, "perhaps someone knows some other information that will make this theory immediately 'void'."
SEORoundtable also presented an interesting thread on the value of links from forums.
Thanks to SEORoundtable for the tip and SEOChat for hypothesizing.