Perhaps these will turn out to be more effective than the current hyperlinks. Like the tabs they replaced, these still seem little used by searchers. If so, they still don't solve the problem that down the line, you can't have a billion icons sitting up above the toolbar. My article Searching With Invisible Tabs article looks at that problem -- and illustrates it -- more.
It would be better in my view if the interface carried through on the results page. I also agree with some of the comments of those discussing the system about wanting to be able to customize what shows up there. FYI, at Yahoo, you can customize the hyperlinks it uses if you make use of the pure search interface and use the edit tabs feature. A9 also allows you to edit the search buttons along the side of its screen. Google offers no customization like this at all on either the Google X site or the main Google site itself. Neither does Ask Jeeves or MSN Search.
The name, by the way, comes from apparently similar functionality in the MacOS system. More about this and the service can be found on the Google Blog from the software engineer behind the interface: Google goes X.
Want to discuss? Visit our forum thread, Google X.
Postscript: See the Where Did Google X Go? post.