The preview panel is useful because Bing has it. It's like Google has set out to...

The preview panel is useful because Bing has it. It's like Google has set out to ape anything Bing does so the only difference is the result quality.

- Bing added a main search page background image, so Google adds one (but only if you're logged in).

- Bing changed the image search to pack images together with hover for info, so Google made theirs do the same.

- Bing added image search parameters like size, style, etc, so Google adds them too.

- Bing added preview panel, so Google added it too.

- Bing moved cache links into the preview, so Google moves cache links into the preview.

...iirc Bing did all these things and more first before Google.