Sometimes it describes something so incredibly well that you have no choice but to use it.
For Example:
/me stubs toe
"FUCK!!"
Stubbing a toe hurts so much that the F-word must be required if you wish to express your distaste at the painful moment.
also, 'fuck' is a good sentence enhancer, but when it gets thrown around pointlessly, and people use the word for no particular reason, it's effect does tarnish a little.
Still, I just love the word Fuck, it's a good word :)