And of course its a huge data consumer if its throwing map tiles at you constantly. Clearly local storage is so cheap and geo data changes so slowly that it seems ridiculous that the phone doesn't just keep a cache and save you the net charges but that doesn't seem to be in the plans.
EDIT: it is currently a "Labs" feature but it is being officially released soon along with the 3D mapping.
I would like to be using a web browser on a desktop, perform a search, get directions, and then choose to have the entire route's tiles sent to my phone. (Along with hotel, gas, emergency responder, restaurant place information.)