As of early 2010, quite a few new cars come equipped with brake override systems, but the systems aren't universal. President Barack Obama's administration recommended, but did not require, that manufacturers include the system in new cars as a response to a massive recall of Toyota models with acceleration issues.
Manufacturers with brake override in at include pioneer BMW as well as Chrysler, which has the systems in 97 percent of its vehicles (only the PT Cruiser doesn't have it). Audi, Mercedes-Benz and Volkswagen also have at least some models that use the technology. By the end of March 2010, all new Hyundais will have brake override, and by the end of 2010, all vehicles from Toyota, Lexus and Scion will use it, too [source: Motavalli, U.S. News].
As more and more models use integrated electronic systems including drive-by-wire rather than mechanical accelerators, it's likely that more models will come with advanced safety systems like brake override. Of course, this system doesn't work if the driver just plain old mixes up the gas and brake pedals, pressing them one at a time. There are some problems technology can't solve.