We did the Med in 2007 with DCL. We felt that our "room charge" ie cruise cost was reasonable. We looked at the DCL shore excursions and it looked like they were charging an unreasonably high price for their excursions. And nightly before the main show in the Walt Disney Theater they remineded us that the only safe way to experince the ports was through their shore excursions. For these cruises the shore excursion desk was a very large profit center.
For example in Rome and Florence (remember the port is over 1 hour away from the city here) they had a "shore excursion" that cost $90 per person - seems reasonable except this excursion drove you into town and dropped you off and then came back 8 hours later and picked you up and took you to the port. We found directions from the port to the train station in Civiccita (Rome's "port") - less than a 10 minute walk. We purchased a pass that got us train service to both Rome train stations (St. Pietro, and Termini), subway and bus passes for less than $15/person (with the $ to euro conversion). We then hooked up with our non DCL tour guide at the Vatican. So for transportation AND a guided tour of St. Pete's and the Museum we paid less than $75 / person. This same tour through DCL was at least $150. What you got for the extra $75/person was a bus picking you up at the port and you got to bypass the hour long line to get into the museum (for some this is well worth the extra $$$). After our tour we took a city bus and saw the Pantheon then went over to the Trevi Fountain, then caught a bus back to the train station and we made it back to the port. We had to be responsible to keep track of the time because we were on our own.
I spent a lot of time on the internet researching the ports and decideing what we wanted to do. ANd I read Rick Steve "Europe Through the Back Door" and his Italy book.
We did all of the ports on our own and never had any problems.