If you have several doorway/spam domains that Google has decided to gray out the PR on, can you hurt a site who's rankings and reputation are solid by 301ing those penalized domains to the trusted one?

This is the question asked by adamclark at SEW. Ian Mcanerin chimes in with some good advice:

...A 301 officially tells a search engine that the old site is now the new site - for better or worse. If these sites have not been banned, are not members of a bad neighbourhood, etc then 301'ing them can only help you. If, however, they are considered to be untrustworthy and then you tell the search engine that this untrustworthy site is now someplace else with a different name, then how that is handled is up to the search engine - but that is what you are telling them...

But, bhartzer contradicts that idea:

I don't agree. If you 301 a banned domain to a domain that ranks well and is not banned the banned domain will not hurt the other domain. If that were the case, then I could get one of my domains banned, 301 it to my competitor and hurt their site and their rankings.

I'm on the fence. Google (and the other SEs) have been known to do shoddier things than this. It could be trouble for the unsuspecting site. If anyone's done testing on this, I'd be very interested to hear about it.