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When I first saw this I assumed the green bars were a signal to the relevance of the results therein (like a PageRank for a SERP), though it's also been postulated they indicate the number of results.
While this is an interesting change, it may need some explanation to average users if it is to be used globally (say, put a small explanation in a box, or a what's-this link, etc).
Also, since it leads to and gives some apparent measure of Image, Local, News, etc searches from a normal Web search, does this mean it'll be plugged into the Image SERPs, News SERPs, and perhaps Local SERPs as well (thus pointing to a Web SERP, as well as the others)? While this might be a helpful addition to those SERPs, it may be more difficult to integrate it into their design (esp. the Local SERPs).
And here's a wild idea ... for users who're logged-in and already do personal search, personal homepage, etc, could google also show a link & bar-graph for Desktop Search, too? I'm sure Redmond would go crazy over that. But, I'm probably getting too far ahead of things for now.
Has anyone else seen this?