A couple of announcements indicating that Sony's upcoming PlayStationHome (site, wiki) virtual world will have plenty of ad inventory:
GameIndustry.biz: "SCEA has announced the formation of an in-game advertising business unit. Although the in-game advertising unit will be responsible for incorporating advertising across all PlayStation platforms, its emphasis will be on PlayStation Home, which 'will present opportunities for SCEA to deliver dynamic, relevant advertisements in game.'" [Oct 8 2007]
In July, Nielsen launched its GamePlay Metrics service which is based on "console data collected from Nielsen’s people meter TV sample (12,000 households with approximately 33,000 individuals), combined with Nielsen GamePlay Metrics’ proprietary audio signature library that matches the audio signatures of tracked games." Even before the service launched, Sony had said it would participate.
Screenshots: PlayStation Home