There is a thread at WebmasterWorld forums named PR on Sites Selling Links on Ebay Dropping which basically describes some people noticing that the sellers on eBay selling PageRank have seen their PR drop. About a year ago, today, it was very popular to fake your PR. There is a thread from WebmasterWorld named Faking your Pagerank from Feb 19, 2005. Fantomaster explained back in mid March of last year how to do it;
The trick itself is quite simple, exploiting a well known loophole in the Google toolbar's PR feature: set up a page and do a 301 or meta refresh redirect to a URL with a high PR (such as google.com ... itself), a process also known as "URL jacking".
The redirecting page will then “inherit” the target page’s PR value, thus giving the impression of being well positioned within the framework of this specific mechanism of content calibration.
Ben, aka Phoenix wrote Obtaining a PR10 - Search Engine Hackers Show Off even early, on January 07, 2005 explaining how this is done and linking to a few threads. And Danny Sullivan wrote about Fake PageRank Detection Tool in October of 2005.
With Big Daddy we know Matt Cutts keeps telling us it is an infrastructure change. He explains that by saying it fixes a lot of the 301 issues and so on. It may also prevent this url jacking method of spoofing your PageRank, IMO. I did not try to reproduce this and test my theory, so it can be just hot air. But it makes logical sense to me.
Forum discussion at WebmasterWorld.