PR and affiliate codes.
 

I am fairly sure this is an open and shut question, but if you link to someone who you are an affiliate of and their link is. www.payment-processor.com/siteid?id=affiliateid or whatever, you are effectively casting a "vote" for payment-processor.com with regards to PR yeah?

Right.

But there's a chance Google will apply an invis nofollow to block juice from passing. Google considers affiliate links to be a brand of paid links. As far as I know Google's policy isn't to penalize you for them though, mainly because, according to a Googler, affiliate links are easy to identify.