As many Android users already know, Google has been collecting voice samples for a long time through its Voice Search app and dictation, and through that Google has learned quite a lot about how users ask for information, which is the key to creating "natural language" recognition. Word has it that the mysterious Google X team has been working on Majel and may release an early version of the update by the beginning of 2012, but that would only bring the natural language update to Google searches. The full update with voice commands would likely become available later next year.
Of course, once the base release is done, it's very likely that 3rd party voice command apps on Android could take advantage of the new features before Google puts out the full release, because most of those apps are built on Google's voice recognition engine. Also, the codename does support something that Matias Duarte had said which was that Google doesn't aim to add personality to the voice system, but rather have everything be voice-enabled. So, it's far more likely if your Android talks to you, it will be called "Android" not Majel.
source: Android and Me