The Zynga Message Center was originally added in April 2010, however due to issues, was later removed. It was added back on September 29, 2010 to a select number of users for bug testing. It allows you to accept gifts, help requests and Neighbor invites without having to leave FarmVille. The Zynga Message Center can be easily accessed while playing Farmville by clicking on the "Farmville Request" sign which looks like a white box with a Z inside a speech bubble. The sign will have a number replace the Z when you have available requests.
Currently, The Zynga Message Center is not available for everyone.
FarmVille Requests Sign
Zynga Message Center Help
Accepting gifts using the ZMC.