Don't waste your money on a factory Nav unit if your thinking that way. It looks great, but as far as navigation the factory nav unit sux. I have had my NAV get lost while driving on an interstate. It tells me I am on an uncharted road. I have had it tell me to turn right and I'm on a highway with no exits in sight. It also told me once that my destination is on the right. Nothing there but a field.
Also, the factory units run off of a DVD. To update the maps, it'll cost you $199.00 plus tax and shipping for a new DVD. I did it once and it set me back $ 125.00 and it wasn't any better than the old one. There are many other Nav units that are much better, can be updated at much less cost and you can download custom POI's from various websites. Can't do that with the factory unit.