i had a very brief noodling with the 2.7's admin interface (which i accidentally downloaded via svn today). a couple things came to mind that i wanted to share...
-- [feedback] i really like the left navigation. i like that it helps bring content up higher in the page, and i find it easier to find my way around the admin area. overall, the interface felt very comfortable.
-- [suggestion] one thing i did notice though was that it was when i was in the settings pages, it was very easy to make changes and immediately navigate to a different tab without saving. perhaps adding confirmation dialogs (like the post edit page) when the form has changed would prevent changes from being easily lost.
anyways, i just wanted to share my thoughts.