Back to that security thing I brought up before...it might be better to mark the entrance to your subdivision as "Home". That way, if your car is stolen, you're not giving a thief directions to your doorstep. And you'd avoid the annoying navigation messages!
If you just bought the car, it's worth at least asking the dealer if they'll give you a disc. It's not like they can control the navigation content, so it's not their fault, but they may have a little sympathy for you.
The next Nav update is due out in November, so hopefully it'll have more of your streets on it.