It would be great if you could make the background of a viewport, for say a legend or key, opaque. This would help when you have a drawing on a title block and you don't want to waste time editing the boundaries of other viewports on the title block. I have not been able to find a way of doing this, apart from using a family to make similar objects.
Below is an example that I threw together for this post.

Cheers
Raoul