Twice I have printed out directions from Google Maps, and twice it has gotten me off track. I think Google must be using an inferior database of roads to generate their directions.
On the way to Salem, my printed directions omitted the fact that I-95 North is the same road as Mass. Rte. 128 for several miles; completely failed to mention that when they diverge, you want to take the left fork and stay on 128; and got the exit number for Peabody wrong.
It's a shame, because Google Maps is pretty good otherwise. Its user interface puts it way ahead of its competitors.
But all these sites have a long way to go. For example, none of the free map sites show highway exit numbers on their maps. And none show public transit lines. Or pay parking lots. Driving directions could also be improved dramatically without a great deal of technical effort. The most obvious thing is landmarks. Good directions periodically reassure the traveler that he's on the right path. "You'll pass Boston Common on your left." Or, "Pass through Joe Bloggs Tunnel." Or, "Turn right on Walnut St. at a large stone church."
The other thing that sent me astray this weekend was the sign on I-93 South (into Boston) that says, "Commuter lane - no exits until Storrow Drive". Actually, the Storrow Drive exit is one of the ones bypassed. I think this has been the case ever since the new bridge opened almost a year ago. It's crazy that the sign hasn't been changed.