GPX Conversions with GDAL 1.6

To extract speed and time values from a GPX track_points layer and create a shapefile:

ogr2ogr output my.gpx -sql "SELECT speed, CAST(time AS character(32)) FROM track_points"

This way you can create a CSV with lat/lng values:

ogr2ogr -f CSV output.csv input.gpx -lco GEOMETRY=AS_XYZ

Kudos to simo on gis.stackexchange.com