Google seems to be testing a new Google Instant search feature named Instant Search Within. I've seen this feature within unofficial search browser extensions but it seems Google is now testing it directly in Google.
How does it work?
You search for some brand and then Google will show you an instant suggestion for brand name plus "search within." As you can see from the screen shot, provided by techno-net's video, this will do a site command search for a keyword phrase within CNN.com.
Here is the video demonstration:
Will Google keep this? I am not sure, they already dropped other search within attempts in the past.
Forum discussion at WebmasterWorld.