Google Transit has been around since late last year, and as early as this February, public transit stops started to pop up on Google Maps, alongside other landmarks and locations, indicating the service was slowly moving into the mainstream. This morning, Google Transit is alive and kicking as a "graduate" of Google Labs. You'll now find a new link on top of your driving directions in Google Maps to toggle the public transit directions, be it bus, train, or boat--assuming you're in one of the 10 U.S. cities (or Japan) with supported transit systems. You'll get a step-by-step guide of where to catch a ride, where it'll drop you off, and when to get there, complete with bus/train/boat numbers, travel time, alternate routes, and fares.
Also neat is the option to turn on the traffic layer to see if your bus is going to hit major gridlock on the way there--helpful if you're relying on above-ground transportation. My absolute favorite feature, however, is the savings comparison. Google Maps will show you how much money you're saving by using public transportation compared to driving in your car. It gets these numbers by computing the mileage by the standard tax-deductible rate per mile, set by the IRS. Unfortunately it doesn't include things like toll bridges (yet), but it's a good way to eyeball if you're better off hopping in the car for a quick jaunt.
The bottom line is that Google Maps probably offers a better interface than your local transit authority. That coupled with driving directions, food recommendations, and the option to save your commonly used routes to use over and over, make it a more compelling solution. Just be careful though, not every transit system in your city could be included in Google's feeds. In the case of San Francisco, Google integrates Bay Area Rapid Transit just fine, however it ignores the inner-city Muni trains and CalTrans long-haul trains, which could lead you to an unfortunate, and expensive, three-hour bus ride.