Since version 0.47, Inkscape no longer ignores filters when exporting to PostScript and PDF formats (which, while being vector, do not support anything like SVG’s filters). Now, any object with a filter applied will be by default rasterized (i.e., converted into a bitmap object) in the exported file, fully preserving the appearance it had in Inkscape (but, potentially, increasing the file size). In the export options dialog, you can specify the resolution of the bitmaps, as well as turn rasterization off, in which case objects will remain vector but will lose any filtering.
When performing export via the command line (C.2 Export), the corresponding options are --export-dpi to specify the resolution and --export-ignore-filters to turn off rasterization.