Love the functionality that RBTray provides and the fact that it doesn't put an icon in the system tray.
Would like to suggest the following new function:
Allow drag-and-drop reordering of buttons of the taskbar. Like, click and hold a button on the taskbar, then drag it to the position that you would like it to be in (relative to the order of the other buttons on the taskbar), then release it - RBTray then reorders the buttons on the task bar.
Just a thought.