One of the oddest behaving apps i think.
When you delete it, then turn your phone off. I have deleted mine before and it wont let me reinstall because it still things it "installed" even though its clearly deleted. A reboot will fix that. One time i updated it on my wife's iphone and had to do a full restore, FB update corrupted things so bad.
I'm still surprised they have not fixed the unreliable push and add sounds for such a popular social network.