Unfortunately, Google Transit doesn't currently support the Safari web browser—but we're working on it! In the meantime, we recommend Firefox for viewing Google Transit on the Mac.
Transit, which builds on Google Maps, gives you step-by-step travel directions using public transportation rather than driving directions. It also computes the cost of the public transportation and compares that to the cost of driving to your destination. Transit currently works only for Portland, Oregon, but Google says it plans to expand the service to include cities around the U.S. and the world.
[Thanks reader Sean Lucas.]