It's so expressive. Stub your toe - "F@CK!!" Nasty horny - "I just wanna F&CK." Bold defiance - "F*CK YOU!" Suburban guy really happy about something - "F^CK YEAH!"
Some people are experts of usage and can rattle off about twenty different variations in a two minute conversation. Other non-cussers can use it sparingly to show serious disdain (i.e. "You're making me go there! F#CK you muthaF+CKer and the F$CKS that made you...Lord forgive me.)
It's just a great cuss word. Any favorites?