Well, I've personally always wondered about the whole PR sculpting/evaporation thing and how that's been put forward by some within Google. Why? First because there's really no reliable method someone outside of the Googleplex Nofollow walls can prove how much or even if a link gets PR Flow Through, partly because there have been some highly conflicting statements put out there and partly because this is one of those areas where a little completely harmless fib on a single Google reps part would then make it simple as it can possibly get for them to tell if a site has been highly optimized. And no I don't optimized well necessarily, just highly optimized. Because PageRank Sculpting should be about the last possible thing anyone should need to get involved in.
Long story short, there's no way to prove if some of the statements made about PR Evaporation are even true. You have to take it on blind faith that it happens. And if you assume it's true and attempt to do anything to control it, your site is suddenly waving a big old red flag that screams out that someone who has control over it is very, very, very concerned about links, thus might possibly also be interested in trying to game Google.
No, I'm not saying that's the case. Just a possibility if this is one of those times someone at Google decided to put some information out there for purposes that might not at first be evident.
In the end, in the US anyway, does any of this really matter?
With the new FTC Guidelines that take effect soon you're supposed to be labeling those affiliate links anyway. And in a way that is obvious to normal users, who won't (generally speaking) be nearly as sophisticated as someone involved in SEO, IM or Search. Given those FTC requirements, again in the US, one could make the argument that the search engines should be able to pick up on the fact that those are affiliate links anyway. No matter how you tried to disguise them.
The whole thing has become a circular argument IMHO. And it makes my head hurt.
So for my own stuff I'll just link as normal, label them to meet the FTC Guidelines so I don't get fined and let the PR Sculpting chips fall where they may.