I wanted to create a custom window, but NSBorderlessWindow is ugly, because you have to implement most of the functionality yourself. Taking a page from Uli, I extended that functionality a little bit.

I present you with my hacky box:

UPDATE:

Anyone who has tried to use the code below, would get this result:

A method went missing. I've added it to the code below.

Notable things:

1. This is just a textured window. All usual functionality (resizing, exposé, shortcuts) is there.
2. Notice the location of the close/miniaturize/zoom buttons. They are moved to the right.
3. The resize handle is also moved to a better location.
4. The window title (aptly named, "Window") is the usual one, set in IB.
5. No borders are drawn.
6. When resized, the image scales with the window.
7. I can't draw :)

To do this, download the above mentioned class, and add the following methods:

- (struct _NSPoint)_closeButtonOrigin
{
    NSPoint point =  [super _closeButtonOrigin];
    point.x += 35.0;
    point.y -= 5.0;
    return point;
}
- (struct _NSRect)_titlebarTitleRect
{
    NSRect res = [super _titlebarTitleRect];
    res.origin.y-=6.0;
    return res;
}
- (struct _NSRect)_maxXminYResizeRect
{
    NSRect res = [super _maxXminYResizeRect];
    res.origin.x-=13;
    return res;
}
// to make the borders disappear
+ (void)drawBevel:(struct _NSRect)fp8
          inFrame:(struct _NSRect)fp24
 topCornerRounded:(char)fp40
bottomCornerRounded:(char)fp44
{
    return;
}

Can't help with the drawing skills, sorry. You have to be born with them.

Of course, all this is undocumented and will probably break tomorrow... But still, it's fun and a much better way than reimplementing everything in a borderless window!