These were put together from all the recent interviews with Toriyama and Square Enix Staff, and compiled by someone over @ http://galmossan.blog20.fc2.com/blog-entry-1406.html. 

Below is all the info!  Enjoy! :) 

• Toriyama says that all frame-rate dropping issues seen in the Demo will be fixed, for the Final Release. 
  
• The difficulty will be drastically increased. Toriyama goes on to say, it's expected that Final Fantasy XIII will be the most difficult Final Fantasy game ever crafted. 
  
• Party Members are completely AI/CPU controlled, in the Demo. In the Final Build, the Player will be able to issue Party Members commands to follow as well as have an interface for managing them. 
  
• Continuing your Chain is not important to finishing the Demo of Final Fantasy XIII. However, in the Final Rlease of the game, it will be absolutely vital to conduct Chains. 
  
• In the Demo, if the very first hit of a Chain ends up killing-off an enemy, the attcking Character will continue attacking the air for the duration of the Chain Combo. This will be changed in the Final Release, so that the Character will stop attacking. 
  
• The classic Final Fantasy Victory Fanfare Music is not present in the Demo, but it will be in the Final Build (Victory Poses are still currently under consideration). 
  
• Subtitles will be added to the Final Release, for NPC's, where there is only voice in the Demo. 
  
• In the Demo, all enemy encounters come from the front.  However, in the Final Build there will be different encounter types, like from the back and/or being surrounded. 
  
• The Leveling System was not in the Demo and will make it's appearance in the Final Release. 
  
• In the Final Release, the Player will be able to add Segments to the Time Gauge, through the Character Growth System.  In the Demo, the Time Gauge currently maxes-out at 3, with no way of increasing it. 
  
• In the Final Release, the "TP Bonuses" acquired after battle will mean something.  These are related to Summons, which will also be usuable in the Final Release, as they are not in the Demo. 
  
• The Final Build will have Command Shortcuts and also an "Item" Command, which is missing in the Demo. 
  
• The Final Build will have a more streamlined targeting system, in battle, than the Demo did. 
  
• Snow Villiers is weaponless in the Demo Version, and attacks with punches and kicks.  He will, however, have weapons in the Final Release. 
  
• Sazh Kalzroy's battle animations are currently undergoing an altering, of sorts, and will be more "jolly" in the Final Release and less "bizzarre" as in the Demo.