Google Labs has expanded its transit planner service to include Eugene, Ore., Honolulu, Hi., Pittsburgh, Pa., Seattle, Wash. and Tampa, Fla. The service started last year in Portland, Ore.
This slick service integrates with Google Maps and lets you plan bus and mass transit trips. You can ask for routes using POIs, such as “space needle to SEA”. It also includes walking directions to get you exactly to your destination.
Google also provides an API for transit agencies to submit data. It’s a Herculean, data intensive task. It’ll be interesting to see how many transit agencies go through the trouble. I would love to see WMATA, the agency that runs DC’s Metro get on board. The UI on Metro’s Trip Planner is awful.
Unfortunately, Google and most of the mapping providers have missed the low-hanging fruit when it comes to transit data: subway stations. Only MSN shows them. (And these have disappeared in Local Live.) This is high value information for city residents and should be on every map.
Rakesh Agrawal's blog 
No doubt, the WMATA site is not so easy to use. I wish it had maps with the directions, especially with bus to metro directions.
I think a good way to get more transit systems on Google Transit is for people to send emails to their local transit system. Although it may take a little work to set up the data in the right format, they’d easily make that back in increased ridership and overall rider appreciation. There is a sample email at http://googletransit.blogspot.com/2006/09/sample-letter.html
Updates:
Google Maps now include subway stations.
https://blog.agrawals.org/2007/03/08/on-the-google-maps-wavelength/
The Metro Website now includes real-time train information.
https://blog.agrawals.org/2007/03/10/metro-live-train-information-on-the-web/