I think one of my favorite PA's came when I was travelling as a jumpseater on a NWA flight. We'd stopped about 50 yards short of the gate. Instead of the usual "please remain seated" comment, the announcement from the FO was "Uh, folks, we've got a few indications up here that some of you have taken off your seatbelts... we still have about 50 yards to go, and we can't move the plane until everybody is securely buckled in..."

I had to suppress my grin when I heard all about 15 different seatbelts go "click."