Just a little survey here...
My N97 has a tendency to freeze (resists touchscreen or keyboard input) for 5-8 seconds at a time during many programs that otherwise tend to run very well, but when I run Facebook full screen it happens VERY FREQUENTLY.
Does anyone else notice this behavior?
Short of uninstalling Facebook and seeing if the behavior goes away, I don't know any other way to trace where this is coming from other than surveying other users.
I suspect that the Facebook app may need some further work.