When I enter the Theme Customizer for Twenty Twelve on a clean install, the “Close” button has one of those unsightly dotted borders around it (focus: outline: none;).
Also, shouldn't there be a “Header Image” panel? I see the “Background Image” panel, but no way to easily upload a header image from the Customizer.
In my testing, once I upload a header image via the dedicated Header panel (themes.php?page=custom-header), the “Header Image” panel also appears in the Theme Customizer, but not until then.
Is it just me?