It depends on how you define success. E.G. PostGIS, GRASS, GMT, GPSDrive, JTS, KFLog, Vis5d, Geotools, GnuGaMa, BBBike and R use GNU GPL; OSSIM, OpenEV, VRS and degree both also utilse the LGPL. All those can be called successful in their area or targetted use.
just a quick correction both versions of geotools are released under the LGPL not the GPL.
Ian