Please check this link to find some unbelievable comparison between digital farmers and real farmers.
http://mashable.com/2010/09/10/farmville-vs-real-farms-infographic/
As you will read this you will realize that even if every farmville player takes out 5 minutes of his time doing some thing like planting tress or saving energy the total time saved would be millions of hours of efforts for mother earth.
So please spread this message and help earth help yourself.