They will begin testing contextual advertising within their network this year, as per the above article. A program for publishers would follow after that.
adCenter is opening in the UK in June, not sure the future for advertisers in other countries. As for a publisher side of things, not much is known about the program at all this time, but I expect it would be US only to start.
As far as i know, Adcenter is already opened up in India.... I have signed up and also paid the 5$ activation fee....still not yet started the campaigns.... 2 days before the launch itself they were promoting in news channels..(NDTV)...