In the thrid panel of the text import druid, the preview area itself does not
provide any indicator that a column's content is to be excluded. The lack of a
check mark on the column header could be complemented by altering the visual
look of the column. This change could include turning the text to light grey,
shading the background of the column (which would not be visible when the column
was selected) or providing a hash pattern in the background (although the
spacing of the hash lines would have to be wide to avoid noise and moire effects
on the screen).

This would re-enforce the role of the checkmark which might otherwise be
confused as a way to select the columns for formating.

--adrian