It works better than Game Commander 2.0, which was my previous standard for voice recognition - I hadn't found anything better up to that point and really didn't need to, since GC worked so well. I wouldn't say it's 100%, but if you learn how to tweak your voice to give it commands, it works pretty dang well. Here is what I have found:
1. Make sure that your commands are being received. You can setup a feedback system to play a sound to acknowledge that the command was recieved and executed. Use that, at least temporarily until you get the hang of it (this includes calibrating your mic). My mic requires me to be no more than 4" away, so if I'm not close enough it simply doesn't hear the command. Having the feedback noise play means that the computer heard me properly. So one of the big keys here is learn how your mic works and how close and how loud you need to be.
2. Enunciate your words. That means speak clearly.
3. Talk slowly. I don't mean slow as mud, but we speak pretty quickly in normal conversation. Talk like you would if you were giving a public speech - slightly slower.
4. Speak the last word higher. Don't ask me why, but speaking the last word at a higher pitch makes the computer recognize the command better.
5. It does help to have a starter command. That means that you have to say a keyboard in order for the computer to perk up and listen to what you say next. The default is just "Computer". So you'd say, "Computer, Get my Mail." This way if you're watching TV or if someone other than you says something, the computer doesn't mistake it for a command.