Announcement Date: September 20, 2012
Effective Date: As of the September 26, 2012 downtime
Valakut, the Molten Pinnacle is no longer banned.
Kokusho, the Evening Star is only banned as a commander.
Primeval Titan is banned.
Worldfire is banned.
You can read Erik Lauer's explanation for the Modern change here:
You can read Sheldon Menery's explanation for the Commander changes here:
Going forward, changes to the Magic Online banned and restricted lists will be announced the Monday each set's paper prerelease. Those changes will take effect during the downtime just prior to that set's Magic Online prereleases.