I have yet to discuss the topic of domain hi-jacking through the use of redirects in detail. Please do not expect me to detail how to accomplish such a hi-jacking of a domain name, that will just make things worse. But this has been a larger problem for at least a few months now. Basically, through the use of redirects, 301s and 302s, you can either seriously hurt an other domain's backlinks or take them away. Again, I am staying very vague.
There is a 34 page thread on this topic at WebmasterWorld named Dupe content checker - 302's - Page Jacking - Meta Refreshes. In addition there is a thread at Search Engine Watch Forums named Come on Google, Fix it !!!. I briefly mentioned this in the Q & A session at the WMW conference (see the last Q & A). Yahoo! has once again said they have fixed the issue and the "changes have been rolled out and will take place incrementally over the coming weeks." Google, I am not aware of any changes being made.