Starting today, we will begin rolling out updates to your Impression Share metrics, which include new ad group-level impression share metrics as well as revised campaign-level impression share metrics. We've also changed the frequency with which we update this data to once a day. These updates will be in effect in all accounts globally over the next few days.
For more information on Impression Share, please visit the AdWords Help Center.
Posted by Andrew Truong, Inside AdWords Crew