This theme is just a very trivial modification to rprobasco's Simplebox theme; the original Simplebox is derived from Clearbox and is distributed under the GPL. It can be found here: http://art.gnome.org/themes/metacity/1148.
As previously mentioned, the changes are very minimal and simple:
* Title text is now centered,
* The colour for title text on unfocused windows now corresponds to the GTK foreground INSENSITIVE colour,
* The gradient on unfocused windows has been softened by about 5%.
I've quickly tested this using other popular GTK themes--for the most part, they're all very decent looking. However, if you are using a Clearlooks-based GTK theme, I highly recommend that you do not use a gradient on your menubar; the gradient of the window decoration and the menubar stacked together looks very, very ugly.
I know these changes are very trivial; however, I was so pleased with the result that I decided to share it with everyone.