Google showed off its new voice search for at Google I/O last week, and now it's available in the the latest version of Chrome.
Chrome 27 allows you to the click microphone in the search box on Google.com, which opens a search page that listens to your commands such as "How old is Robert Downey Jr?" you can then follow the question up with "What films has he been in?" and Google will remember that you're talking about Robert Downey Jr. It really is smart. The new voice search will soon offer the ability to just say "OK Google" rather than clicking the microphone.
As of the time of this post it seems to be having some problems so it may not be fully functional right now.