What open source code?

I would like to see some proof of the open source code that Google has 'absorbed' without contributing back to it. Google has licenced products and turned them into their applications, has financed a large number of projects under their 'summer of code' and indeed has an open source website at http://code.google.com/oss.html. Google doesn't make everything it produces open source, and is perfectly in its rights to do so, and I think it's rather dangerous to imply that they use open source tools to make closed products without supporting the implication.