Peter Kafka from AllThingsD estimates that the deal is in the $70 million range and that Google intends to keep Invite Media running as a separate unit. As Kafka points out, this makes sense, given that Invite Media's customers expect to be able to buy from multiple exchanges, including Google's AdX.
The plan would then be to integrate Invite with DoubleClick for Advertisers for those customers that want to use the ad-serving and ad-buying technologies side-by-side. This isn't dissimilar to what newly-acquired AdMob does with AdWhirl in the mobile space. The difference is that in this case, AdWhirl doesn't handle ad-buys, just the ability to support multiple ad networks within an app.
From a business perspective, it makes sense for Google's ad strategy to expand to other ad exchanges. After all, if a customer is ultimately using a Google dashboard and Google ad-serving technology to buy and display advertisements, where those ads are purchased isn't necessarily of upmost importance. Plus, customers get the ability to bid on ads from different exchanges, without necessarily having to use multiple services.
[img credit: TheTruthAbout]