This is an extension to provide a minimal (Google Chrome-like) status bar for Safari. It also has built-in longurl support to convert those pesky and opaque short urls to long ones again.
File a bug or feature request and I'll try to get to it.
Download the extension and open it with Safari. Also, you'll probably want to hide the real status bar via View > Hide Status Bar (⌘/).
Looks just like it came with Safari.
People use Safari because they like how it works and looks. Keep to the same promises. This means no themes, no customization other than what you very likely already want. If you want customization, try Ultimate Status Bar.
If you're here, it's because you want a useful status bar. Shorturl lengthening and other info is appreciated, but should balance intrusiveness.
This will follow the latest versions of Safari, meaning if Safari changes look and feel, this will match only the latest. You might try previous revisions if you're trying to match older Safari versions.