Mockup for the panel: I think one of the Xfce weak point is that the interface is unattractive. The panels and squares and goodies are very serious. Maybe that's one of the factors that make the Xfce desktop environment very light, but opaque beauty.
Usually users delete one of the panels. That is why it would be good by default Xfce 4.8 includes a single panel, and gives the user the ability to add another, only if requested.
It makes no sense to move the panel freely around the desktop, I think it is better than the panel is fixed at the bottom or top of the desk.
The panel can display only the rounded edges on the end that is inward desktop.
A tray with rounded edges give you style and beauty to the panel, also highlighting more elements.
Square edges on the window list are somewhat ugly. I think that the rounded edges are prettier.