Zynga pulled off FarmVille from MSN Games portal. The departure from MSN looks much more notable, Inside Social Games, speculates that the "Microsoft platform possibly not producing enough traffic to keep Zynga interested," but given the volume of about half a billion monthly users worldwide between Games and Messenger of MSN, that seems a bit of a stretch.
Microsoft issued a statement about the mysterious disappearance of FarmVille from MSN: "Farmville isn't currently available on MSN Games," Microsoft said. "We've a great relationship with Zynga, and will continue to work together to provide robust games experiences for casual and social game players in future." But declined to say why, exactly, Farmville is gone.