Photo of the new Metro-North Yankees-E. 153rd St. station from this site.
There has always been good subway service out to Yankee Stadium, but now there is a new railroad service and a new Yankees-E. 153rd St. train station to make things easier for the suburbanites (how often does one hear about a new train service and a new train station?):
From the Northern Suburbs:
Take Metro-North Railroad to its new Yankees-East 153rd Street Station; there's direct weekend-game service from the Hudson, Harlem, and New Haven Lines, as well as weekday service, and shuttle trains from Grand Central. Click here for details.
It's a great amenity for folks in Westchester and CT, because the traffic and the parking have often been discouraging for them.
How well does the baseball transportation work in Boston?