The dedicated transit apps (we have one for the busses in Brighton and I've used the tube app in London) are great for providing location-based information on the go. What they're no good for is pre-planning a journey between bookmarks or contacts' addresses that involves a mixture of walking and one or more changes of public transport. The Maps app in iOS 5, with google's data, is splendid at this sort of task. The app in iOS 6 is hopeless.