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)
Today's scientific question is: What in the world is electricity? And where does it go after it leaves the toaster? -- Dave Barry, "What is Electricity?"