Hamish:
> Enable the GPS plugin, then Plugins->GPS->Create new GPX layer and
> save as filename.gpx.
eeh, check that actually works- for me it wrote an empty file.
I'm using a really old copy of qgis though (8.1) so hopefully it works
better now. the points will be saved in the shapefile so no data loss,
and ogr2ogr will do shp->GPX as a work around.
Hamish