Can I train Google Voice Actions to better recognize my voice?
You could try enabling the "Personalized Recognition" option in the Voice Search settings. This option basically causes Voice Search to store words and phrases that you use on your Google account, and gradually build up a voice library of your speech patterns. You can read the original announcement for it on the Google Mobile blog. 

I believe this feature is only available in the US on Android 2.2 or later, but it's possible there may be other restrictions as well.