(Note the preview size does not grow when you do this.) But for files with long paths (which introduce a horizontal scroll-bar), it sometimes becomes impossible to resize the last column. You can still grab the side of the window and resize the last column.
In 10.7.5, that separator went away, which is fine for files that have a short path from the left-most column to the right-most column.
The preview would grow to fill as much space as possible. I don't know if it is also a problem in 10.8, but in 10.7.4 there used to be a column separator on the right side of the last column containing the preview with a little area at the bottom that would allow you to grab the control and resize the preview. As hints go, this one is more of a bug complaint than a hint, but the most recent version of Lion (10.7.5) introduced a bug in the Finder when in Column View which prevents you from resizing the last column/preview for files with long paths.
