There is an interesting WebmasterWorld thread named Affiliate ID's removed from the urls on serps. In that thread, the affiliate describing how he achieved top rankings for a merchant. The listed URLs were to the merchant's domain name, but appended to the URLs was the affiliate's ID. Then recently, the affiliate IDs were scratched out of the Google SERPs and the affiliate was no longer getting credit for sales.
The affiliate asks was this something Google did or something done by the affiliate? It is hard to say for sure without having more detail. I would assume that if Google dropped the affiliate URLs, the rankings would drop as well, unless Google did a wide spread affiliate URL bashing. It is more likely something done on the merchant side.
I contacted the sponsor and I showed him proof of how his listings were showing up for some of the searches targeted. Although it is always tricky to pair a result with ones own efforts, I was able to provide him with information on how the linking took place, during which time period and how his site started to show up originally (under my code) and how it progressed over time. I kept detailed stats on searches as well as screen shots throughout the relevant period.
The sponsor was convinced that he now gets this great traffic due to my effort but has said no word on crediting me for it, specially now that the urls listed have NO partner Id. He must be thinking he is getting mana from heaven without any sweat, my sweat. I went a step further and showed him how Google still lists a url that was read as text, but whose content (and final destination) is actually different. No redirects here, although clicking on that link does redirect.
His excuse is that Google is the culprit. He blames the whole issue on Google. He says -very politely- that he has done nothing on his end to have the redirect listed and not my affiliate link -a flat url with no query strings-. According to him, Google has been undergoing some changes in the last week or so and as a result, they now list the bare urls. In other words, 'swallow it, that traffic is now mine'.
Currently, no one really replied with support that it was a Google action or that it is more likely an affiliate action. I personally wanted to draw more attention to this WebmasterWorld Thread.