EVCin

Successful viral marketing promos in FarmVille have been quickly passed along to two other Zynga hits: Cafe World and Mafia Wars. Whether they will see similar traffic boosts remains to be seen.

FarmVille bucks the no-growth trend, passing 30 million by twisting the “gifting” mechanism from sending gifts to asking for gifts.

Looking back at Facebook’s changes to how application developers could use the platform, developers have mostly complied with prohibitions forcing users to give gifts before playing the game on first and recurring visits. Yet the largest developers seem to still be allowed to gate content (like land expansions) based on the number of friends a user has – continuing to put pressure on people who do not want to spend money to extend their social graph to potential strangers in order to unlock content.

Facebook started enforcing a slew of application policies over the last week, forcing game developers to revamp their viral marketing. Here are three of the top changes and how top developers are revamping their viral marketing tactics.