The 1600px width is a limitation of the particular skin, not a bug. RadToolBar supports any width. If one needs a larger width for a specific scenario, he/she is absolutely free to customize a given embedded skin or create a new one.
I am attaching a sample web page + a modified version of the Office2007 skin, supporting a width of up to 2400px. Actually, only two images have been expanded - ToolbarBgH.gif and ToolbarBgHTR.gif. The CSS code is the same.
the Telerik team