I've seen that "Speak Now" option in other Google product like Google Translate...a good idea that could be useful for those who don't know to write properly or have some kind of disability... the main disadvantage is that is not always very accurate, nevertheless this is a good addition. At this point the 'Voice Search' is only available on the desktop maps....for the online maps,as far as I can see their is no such option.
Btw Google Maps are awesome ,way above the competition.