Voice Search from mobile is now available on your desktop on google.com in English. From the official Google blog:
We first offered speech recognition on mobile search, but you should have that power no matter where you are. You should never have to stop and ask yourself, “Can I speak for this?”—it should be ubiquitous and intuitive. So we’ve added speech recognition into search on desktop for Chrome users. If you’re using Chrome, you’ll start to see a little microphone in every Google search box. Simply click the microphone, and you can speak your search.
And why does Voice Search matter? Well, it’s for showing off, that’s for sure, but you may find it useful for hard-to-spell searches or complex ones that you can speak aloud faster than type. After all, we first learn to talk before we learn how to type, right?