Originally Posted by MDtR-Chicago

This is actually not a terrible idea. The farthest forward exit of the BART station at Embarcadero, on the left side, is directly below the Hyatt Regency at the Embarcadero. You'd walk out of the station half a block to the lobby and there are always taxis waiting at that hotel, in my experience. It has an on-street taxi waiting area that holds roughly 5 taxis.

But I would make sure you map out how much time this will take because there would be a significant amount of backtracking depending on exactly where you are going... you're adding about 10 minutes to the train trip then 10-20 minutes to the taxi ride.