The new transit directions functionality gives you routing for public transportation systems in select markets. I haven't yet tried it out in the Seattle area, but we have a fairly new bus and rail system so I am not confident there will be much for our area and imagine support will be there for areas like Washington, D.C., L.A, New York, and other large metropolitan areas. Simply go to google.com/gmm in your mobile browser to download the latest Google Maps for Mobile client. Thanks to Nokia Conversations for the heads-up on this release.
UPDATE: I installed this on my Nokia E71-2 and it does support local bus routing here in downtown Seattle. The program even tells you (and shows you with an icon) that you need to walk to a specific bus stop to catch the bus, with departure and arrival times. It didn't calculate a transit trip from Seattle to Tacoma though so I need to keep exploring how much is supported. There are Sounder trains and Sound Transit buses from Seattle to Tacoma and hopefully these will be added in the future. Still it is a nice feature to have downtown and pretty amazing that they integrated it all into a free client application.
Have you tried it yet on your device and if so, what are your experiences?