I think that expecting users to flee a service following troublesome changes is unrealistic.
I disagree, think of Friendster, or even Myspace...the social networking crowd can be fickle, if facebook screws up that leaves a market opening for a competitor (ie. Google, Microsoft etc)
We warn the reader in advance that the proof presented here depends on a clever but highly unmotivated trick. -- Howard Anton, "Elementary Linear Algebra"