The printer Lightning Source Inc. will only accept print files for book covers in the form of PDF X/1-a:2001 or TIFF. Neither is available from Inkscape 0.48.2. While conversion of a png file is available through ImageMagick or GraphicsMagick this requires use of the the command line which the current generation has been taught to fear. So I wonder if one or both options could be built in to a future version of Inkscape. Perhaps this could be a GSOC project.