My concern about Zynga is that they're going to burn through users.

People will pay for things in a game and have fun doing it. Then they'll get sick of that game and move on to the next one. And they'll buy more things there, and then they'll get sick of that game and look at the next one and realize that, hey, this one is pretty similar. And maybe it isn't worth investing hours upon hours tending to some sprites. Or forking over real money.

I'm not saying this is guaranteed, but as someone who has played a lot of games growing up, I had it happen plenty of times. Zynga needs to release some games that feel totally different from Farm/City/Frontierville.