Games like Farmvile are not so much games as they are scams to get ad impressions. If you set up a website that had a big button that said refresh and everytime you clicked it you refreshed the page adding ad impressions, you would be summarily kicked from whatever advertising network you use. If you however make a game that requires you to go to a different page in order to DO ANYTHING then you are ok. Zynga and other "game" networks like it are just rushjob crapware that is poisoning the real game industry and is giving facebook and other social networks a bad name for time wastage.
I don't have a problem with social sites, social sharing or micropayments but please, if you are going to take up mine and others time, please be a game, an actual game. Farmville is like a bonzai tree that if not trimmed daily whithers and suggests you buy another one.