Google seems to be testing a radically changed image search user interface. Reports on various websites say that it might have been around for up to a week... and that it looks a bit like Bing. I just got the new interface this afternoon. And I don't use Bing.
The new look page focuses entirely on images, removing all the additional data which was previously displayed under each result. That data isn't gone completely, though. It now displays when you mouseover an image. The page also automatically loads more results as you scroll, kind of like a Twitter app that loads older messages the further down you go. In all, it's an attractive new way of presenting image search results.

Clicking an image is a different matter, though. This action now loads the source website in an iframe, with a slightly opaque layer on top of it, and the image highlighted and expanded. There's also a section to the right of the page containing the relevant image's info. Clicking anywhere in the main part of this page forces the image source page to load. This part of the new UI experience is less positive - it feels like the user is expected to know how it works bef0ore using it.

Expect this interface to continue to evolve as Google continues its tests. The second-step page, which displays the image in its original location, is in particular need of work.

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I like the infinite scroll, but the supposedly "clean look and feel" is only clean because they cleaned out lots of very useful information, like the URL, Size and text snippet that you must now hover to each picture individually (with a short delay!) to see. That information was a key element in doing a serious search, providing contextual cues to the user that guided the choice of which image to open. It will be sorely missed. As I recall, Google already tried to remove the context a while back then put it back in after users protested (I know I did). I sure hope they do the same now!
@Nathan - That's a really good point. You can get the sizes to show if you click the option in the left navigation pane. The other things (like URL and filename), you can control using search modifiers. It's not perfect, though, so maybe they'll bring back the 'classic' look as an option if you complain loud enough!