I just got an email talking about this Jeet Kune Do "Lead Punch" System. Its a book about "How to use Bruce Lee's principles to better your lead punch, no matter what your martial arts style!"
"Holy crap an entire book dedicated to throwing a jab...a must buy!"
I believe that the lead hand straight and jab are actually "different" punches. A long time ago I asked about it in rec.m-a and Frank Benn did a really great answer.