@Linkat,
I have a data plan which I never exceed, so I never worry about using the data features when I need them.
That being said, I agree that Siri isn't always so accurate either. There are occasions where I need to pull over and key something in to find it, but I would rather do that than call 411.
I usually give Siri a chance while I'm driving to see if I get lucky, then I pull over if that doesn't work.