Re. Google PageRank - other search engines use various kinds of link-pop too, so I assumed Google were doing what what other log spammers do. However, as I said earlier I find it hard to believe Google would do this, but I have this stuff recently appearing in my request-report.
Its not a referrer thing its a request thing i.e. my logs have always shown requests (not referrals) for ebay, yahoo and a bunch of other sites. I have always understood this to be 'log spam' where the spammers want links to their site to show up in your 'request report'. However perhaps this proxy thing sheds more light on the matter.
There are probably lots of people here who understand this insideout. Can anyone explain a bit more about this?