In a couple places their reported stats wildly differ - which is a little disconcerting.
But they do agree on this:
A page with zero backlinks can have a PageRank of 2.
A page with 2 backlinks can have a PageRank of 5.
A page with hundreds (or thousands - the stats differ) of backlinks can have a PageRank of 0.
You can look at this yourself. The search term is:retro sunglasses
I always thought of PageRank as an evaluation of how important a page is - primarily based on links to the page.
But can a page be considered important if it has no links?