Lived in the Panama Canal from 1980-1982 in Gatun (Atlantic side). My in-laws are taking a Carnival cruise in April 2003 beginning in Ft. Lauderdale, going through the Canal, stopping in Costa Rica and Mexico and ending in San Diego, CA.
They did this same route (on Princess) several years ago and they love the temperature, the varying sidetrips available (canopy trips, horseback riding, SHOPPING!, etc.,) and they say the people they meet seem to be "genuinely" friendly (native peoples).
Some of the places they are going to hit this next trip are: Cartagena, Costa Rica - Mazatlan/Acapulco, Mexico. They are very excited.
Hopefully, someone with more current information will leave a post for you!
Kitty