Carlson Survey has a very nice routine for adding scale bars. When you have your drawing set at the proper scale say 1"=30', when you insert a scale bar, viola! the scale bar comes in at 1"=30'. And if you need to add another scale bar for another view port, say an area you want to show more detail, change the project settings scale to 10 scale and boom! the scale bar comes in at 1"=10'.
Ron Mak commented
If/when intellicad comes out with dynamic blocks, this will be a better option.
A larger choice of scale bar types to go along with it.