This CNet article indicates that the MPEG-4 Licensing terms are still under negotiation. Quotes from both Steve Jobs and the vice president of the MPEG LA indicate that they believe that the terms will be worked out by Quicktime 6's official release:
"The licensing stuff is getting worked out," Apple CEO Steve Jobs said in an interview Tuesday. Every 'i' is not dotted and every 't' is not crossed, but it's getting there. I have a lot of confidence it will. This is too important not to get worked out."
"We don't have any new information on the licensing, and we hope that we'll have final terms sometime this summer," said Larry Horn, vice president of licensing and business development for MPEG LA. "That being said, Apple's announcement shows great confidence that a reasonable license from all the various patent holders will be available."