Check out this video from TLD comparing Google voice search and Siri.
We are more than impressed by Google’s voice search on iOS. Testing it out on the iPhone 4 (without access to Siri) we found it to be almost flawless. You can talk completely normally, within the confides Google’s search results, and the reaction from the app is pretty much instantaneous.
We also felt a lot less limited by our location factor (Cape Town, South Africa) when trying stuff like location searches as you might do with Siri.