It sounds like a good idea, at first: programming your GPS with the Sith Lord's dulcet tones so he can tell you when to turn and when to stop. But how long before all that heavy breathing gets insufferable?
We might've been a little hard on ol' Darthy recently, but we've still got a lot of love for the former Anakin Skywalker. And the idea of TomTom offering customizable Star Wars voices for their GPS units is pretty cool — but I've gotta think the shelf-life of that coolness will expire after your first "I'm lost" experience, where you just want someone to tell you how to get home.
And I'm fairly certain that having C-3PO (who'll be available soon, as will Yoda and Han Solo) talking at me for hours would be a legally defensible cause for road rage.