We did this cruise this past February 7-17, 2007. We did not do any excursions in Panama but stayed on the ship until we docked @ Colon. Then we went inside to look at all the native handicrafts (some quite good & expensive) and watch a show of native dancing. Beware, the women were topless.
We did however take a tour w/Charlie Soto in Costa Rica which was more comprehensive and cheaper than anything the ship offered. Then in Montego Bay we booked a private tour w/Barrett's Adventures for $35 pp for a six hour tour. We told Chester, our driver what we wanted to see and he took us there. Again it was far and away better than what the ship offered. I do have a review posted on this site if you want more detail.
We also did the Coral Panama cruise and stayed on the ship for the transit in and out of the locks. Did you check out the excursions offered by Princess, they probably have something you would be interested in. If you do leave the ship for a tour, they tender you off in Gatun Lake and then you rejoin the ship at the next port. Enjoy!
Princess Cruises x 7
RCCL x 1
Carnival x 2