Google acquired Postini back in 2007, then slowly transitioned features from the hosted security and archiving service into Google Apps. Back in August, Google provided an update about the plan moving forward, noting that it planned to have Postini fully transitioned into Google Apps by the end of the year.
At the time, Google released a minute and a half-long video about the transition. With the new year, Google has now posted an hour-long presentation about the transition complete with an update, an overview of the transition, a look at the Google Apps platform, and a Q&A session taken from customers.
Google notes that some of the content in the video is forward looking, and is subject to change.