This is a feature that I would love to see go into QGIS. I waste a great deal of effort and space by generating shapefiles from my DEM files - one shapefile for 20 and/or 40 foot contours, one shapefile for 100 and or 200 foot contours - then have to load up the separate layers and manage them independently in QGIS.

I would be nice if I could just select a checkbox on the display properties for a DEM file in QGIS, "Display Contour Lines", and specify the contour interval and line properties.

Here's how I currently generate my contour shapefiles on the command line:

gdal_contour -i 100 -3d -snodata 0 mydem.tif mydem_contour100

This generates a 100 foot contour shapefile, where each line has an attribute specifying its elevation, 0 is the "no data" value in the DEM.