At the moment, we are playing a D&D Renaissaince/7th Sea kinda cross in the office campaign, and one of the players took a Gnomish Chaos Mage (to go alongside his brother, who was a regular Wizard). The biggest problem in session one was that the player had not read the rules in their entirety, which resulted in him trying to do things that are just not allowed! The second session, however, was better, as he had several 'prepared' spells and was able to take a more active role.
Moral of the story - know the rules, as this character is nothing like a regular Wizard or Sorcerer!