Google announced they are making changes to the ad click referrer to help speed up the click and make it more consistent from property to property that ads run on.
Google said the change won't impact Google Analytics tracking but if you do your own tracking, then you should be aware of the change. Starting in July, they will be testing the new referrer string but in August it will switch over 100% to this new referrer.
Up to now, referrers for clicks on ads for the term "flowers", for example, would be one of the following:
Google is now adding a third possible referrer:
The query is still as the GET parameter 'q' and the originating host for the click is there as the GET parameter 'ohost'.
We're making this change because we're trying to improve the experience of clicking on an ad for our users. For historical reasons, Google currently uses two redirects on two different domains for many of the ads on our site. We are streamlining our infrastructure to remove one of these redirects, which brings users to ad landing pages faster, leading to a better user experience for our users and a better return on ad clicks for our advertisers.
Forum discussion at WebmasterWorld.