Hi Rob:
iOS 5's default voice for English is Nuance Vocalizer Samantha.
You can get a higher quality voice Jill.
Go to Settings> General> Accessibility>VoiceOver and turn "Use Compact Voice" off.
Stay connected to wifi, best plugged in, after a while system will download Jill as your default voice.
If you decide you don't like the voice just turn " use compact voice" back on.
Regards,
Jim, East Lansing