Google has achieved impressive accuracy for speech-to-text (especially for open-domain large vocabulary speech recognition).
If you use Google Web Speech though, you receive text and you still have to do NLP to "understand" the user intent. The other problem is, if Google does not know about specific words (like your company or product name), you have no way to customize the engine (no "Add to dictionary" entry point in the API!).
Google's Web Speech API can also be used to build something similar.
Here is the Web Speech API Demonstration: https://www.google.com/intl/en/chrome/demos/speech.html