Operation Burnout reports that on Xbox Live you can now purchase and use cars that were not originally slated for release today. In addition to the Legendary Cars that were scheduled for release today, The Toy Cars pack, the Boost Specials pack and the Time Savers Pack are also available for purchase.
Criterion Games have confirmed that this was a mistake on the part of Microsoft and that they had no intention of releasing the additional content today. Matt Webster from Criterion Games has stated on his Twitter page that "we're not happy with Microsoft (again)".
We'll keep you updated as to the availability of these cars on PS3.
Microsoft has corrected the error and removed the additional updates from Xbox Live. Those that got the updates while they were still available will be able to continue using them.