Today I had a problem where the ScrollViewer in my user control would not scroll using the mouse wheel unless it was over a control like a textbox or label... anything other than the grid that is LayoutRoot.  It went something like this:

After much trial and error, I figured out that all is needed is a background... it can even be set to Transparent. So, I did this:

I know it is simple and probably makes me look like igmo, but I thought it might help somebody else one day. :)