We just got back from a cruise with Princess thru Western Carribean (Grand Cayman, Costa Maya & Cozumel). I booked our own excursions for Grand Cayman & Cozumel. Found a lot of info thru internet, starting with ask.com for info by port. Travelnotes.com was also helpful. Both excursions went really well - stingray swim/snorkel in GC & jungle jeep tour in Cozumel. We used Princess excursion to Uvero beach for Costa Maya & it was a complete waste of money. Took a bus (picture Romancing the Stone) to a decent (not great) beach with free (but really cheap quality) drinks & not much more. Lunch = $6 cheeseburger/ $4 hot dogs; one shop; there were waverunners available. To answer your question Pros to me were cheaper, less crowded/more personal. Cons would be mild stress at getting back to the ship on time. All the companies we dealt with were reputable & used to dealing with cruisers so there was never any problem or question of getting back in time. I saw many people with signs for impromtu excursions at each port but I don't think I would have been comfortable with most of them. Hope this helps. Pat