We are getting reports about the USGlobalSat and DeLuo USB NMEA GPS receivers not working when users have upgraded to Mac OS X Leopard.
USGlobalSat have addressed this problem and new drivers are now available from their site: http://tinyurl.com/2nafcf
DeLuo have also addressed the problem and you'll find their drivers here:
http://tinyurl.com/2j7w3e
Neil