setting a custom app for the car dock?

An app would have to be written to "listen" for when the phone is placed in the dock. Without that, an app cannot load upon insertion into the car dock by itself.

You could do this with Tasker, maybe Locale, and there my be other apps that specifically let you choose which app to run upon insertion in the car dock.

 

Vlingo does have an option to autolaunch when any bluetooth device is activated... if you only use blutooth in the car this solves the problem.

As far as android's ability to support this feature, it already does. I have an aftermarket car home app installed that takes over when put into the car dock; I also have an aftmarket application that takes over when the phone is put into a desktop dock. It is up to vlingo to implement this as a feature, it is already supported by the OS / API.

I'm sure that if you request it directly with vlingo you will see it in a future update (..I had some support questions / conversations with them in my blackberry days and found them to be very responsive).

 

I think my use of the word "listen" misled you. I didn't mean to imply that the app has to be running in order to load when the phone is inserted into the car dock. I'm not an Android programmer, but my understanding is that if an app doesn't "declare" that it can respond to dock insertion, then there's no way to tell Android to load that app upon insertion. I believe this declaration is made at installation time, but does not require that the app be running at the time of insertion.

 

BlueDock - Android app on AppBrain

I don't use it so don't know if it will do what you want but it looks like it may.
I do use Car Dock V2 and Car Dock Settings and they work well.