When you scroll the mouse-wheel over the desktop to switch workspaces when using another window manager like openbox it moves 2 spaces rather than 1. I beleive this is because both openbox and xfdesktop provide this feature. It would be nice if it was possible to disable this feature in xfdesktop.
Nope, xfdesktop passes any unhandled key or scroll events to the root window. With a full Xfce desktop running, xfwm4 handles desktop scroll events. Unless you're running xfwm4 (which I imagine would be quite impossible with openbox running), nothing in Xfce is causing this.