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tedster - 1:11 am on Oct 26, 2007 (gmt 0)
Looks like these may all be in use selectively, according to whatever "logic" Google has decided to use in each individual situation.
Soon after Google started talking about paid links, Matt Cutts mentioned all kinds of options that Google had available technically. For example - stop PR from passing on a complete domain, or a page, or just one link.