Just to add:
The regular Firenzecard no longer covers transport; you have to purchase the Firenzecard+ additionally for that.
http://www.firenzecard.it/index.php?option=com_virtuemart&view=productdetails&virtuemart_category_id=13&virtuemart_product_id=128&lang=en
As Sun-Baked noted, though, Florence is pretty compact so we just walked everywhere.
Even with the cards you still have to make advance reservations for some attractions, such as the Borghese in Rome and to climb the Duomo's dome in Florence.
The passes do not cover getting to/from the airports
Breaking even on the 72-euro Firenzecard can mean cramming too much too quickly into its 72-hour lifespan. Increased tickets prices for temporary exhibits can make a difference, though. For instance, tickets for both the Uffizi and Accademia are currently running 4.50 euro more apiece than normal because of special exhibits through September and April, respectively.
The transport piece of the Roma Pass wasn't a big enough benefit for us as, while Rome is larger than Florence, it's a city that begs to be seen on foot if at all possible. It was less expensive for us to purchase individual tickets for the very few times we chose to use the metro/urban train (we've never used the buses) to cover longer distances more quickly. If you do intend to use transport more often, then the pass may make economical sense.
In short, you have to do the math? Make a list of the attractions you wish to see that have entry fees, add them up, include an estimate for how often you'll take transport, and then weigh that against the price of the pass. We'll often spend longer amounts of time in some attractions than many tourists might so we personally have to consider how much we can fit into a day.