TrueHoop published a fascinating article about the "signature moves" of several of the game's top players. Rajon Rondo's stand-still-fake-pass was one of them. But so was Paul Pierce's funky pull up.
Pierce isn't particularly quick, so how is he always able to get space for that jumper? Part of it is that he sometimes uses unorthodox footwork in his pull-up. The natural motion for a right-handed player moving to his right is to stride-stop, plant the (outside) left foot, plant the right (inside) foot and fire. But Pierce uses his outside right foot to stop his momentum, then uses his left foot and left shoulder to nudge his defender and create space. Pierce ends up firing the shot a half-beat earlier than his defender expects and uses a little muscle in the process.
I think this is just one example of Paul's vast array of old-man tricks. He's become that guy at the playground who looks too old and slow and gets taken for granted until he drops 5 straight buckets in a row. Then some bigshot says, "I'm checkin' him now. Let's see him score on me." And then he drops 3 more on him for good measure. At least that's how I see him.