The navigation bar looks awful in some browsers

[JW]

In Firefox, the navigation bar in the Admin Center works perfectly, but in some other browsers this is less.

Konqueror shows the navigation bar as intended, only sometimes transparent borders above the second bar appear, separating the first level of the second level.

In Opera, em values behind the comma are ignored, so all paddings (all between 0.1em and 0.9em, apparently) are displayed as a padding of 0em. This needs to be re-worked.

MSIE is yet to be tested.

[JW (jw-00000)]

Maybe, the section titles should be made clickable too, because they look like links and it seems like users would expect them to be links.
It could also save you some time, because for example, when you want to select a new theme, you have to move your mouse to the right to select "Themes", and then completely to the left again to select "Manage themes", the only tab in that section.

[JW (jw-00000)]

The navigation's CSS is reworked in the improved-navigation-bar branch, and this code is tested on quite a few platforms already (I'll test even more extensively today and tomorrow).
Making the controller names links wasn't hard either, since all AdminControllers have "index" actions, which redirect to the correct default action.