Anyone Use an in Dash Navigation Unit\Radio?

Thinking about upgrading my car radio, I want one that fills the entire hole where the factory radio is, (double DIN- tech speak) which are usually DVD players/navigation. My dilemma is do I want/need/use navigation enough to justify the additional $300+. I get around town just fine without it but think it might be handy to have.
So my question, do you use yours? How much? Is it worth the cost?