I agree that the female voice sounds utterly put out that you missed that turn she told you to take. I have the Nuvi 660. Garmin refers to the female computer voice as 'Jill' - - they also have a masculine voice, 'Jack'. It is probably sexist of me to say so, but when he says, "recalculating", it doesn't sound nearly as disgusted as Jill does. My wife even agrees. We also agree that he is easier to understand.
The computer generated speech [TTS, text to speech] is sometimes awkward and may be hard to understand if you didn't have some idea of what they are referring to. For example, it might say "turn lef ton highway 437", instead of left on 437. Still, it has been a great help when I'm in unfamiliar territory.
Jack