If there was a decent competitor to Facebook who had a lot of uptake (or even a more "open" networking system), now would be a good time to take advantage of all of Facebook's negative publicity.
Right now I don't see anything good enough to start a transition away from Facebook, even if many people wanted to move elsewhere.
Social Networks tend to be regional, bebo for europe, myspace in the US, friendster & hi5 for South East Asia, Orkut for Brazil, etc. If you decouple your game enough from social networks you can make them work on all of them and perhaps add incentives to use the more profitable networks over others. (10 Facebook credits only gets you 5 farmville points, but buying direct on farmville gives you 5 farmville points for the same price as 5 facebook credits, etc)
There are two questions this brings up to me, in relation to your points.
1) At one point are people willing to give up on Facebook w/o an alternative in enough numbers to seriously hurt the site.
2) How big is the time window that FB has to fix the problems before a competitor automatically could become a serious threat simply because of how fed up people are?
Right now I don't see anything good enough to start a transition away from Facebook, even if many people wanted to move elsewhere.