does anyone have this book and is it worthwhile buying ?

I personally would not waste my money however because I'm not big on the JKD "straight lead". It's better just to learn to jab IMO.

Its a old Kung-fu and other MA idea of striking the opponent with the closest weapon I agree with that.

Some say and I have read Bruce Lee was big on that and felt it could be as powerful as the rearhand. Dare I say it for speed I agree, but for power I disagree with Bruce Lee, throw all the cans and toleit paper you want, I disagree with that. It takes too much training to develop that kind of power on the front hand (unless a hook like technique) when you got something that happen naturally the rear hand.

JKogas right a good jab is all you got one for speed & one for power.

I think the idea of the jkd straight lead is a good one, but rarely do it in sparring since it is more likely that you can get hit with the counter if you miss. I think it probably could be as powerful as the cross, but only if your stance is square or if you have torqued in the opposite direction first.
I agree as well, there's one for speed and one for power, and its probably the same for all your shots.

Mabey it also has to do with the energy flow through your body when doing the punch like being lose until the last second. its almost like phsyics with kenetic energy. i think its just about troughing the punches with correct form vs non correct form. if people through a bad punch no matter how strong they are its not going to do damage but anyone who threw a punch with near perfect tecnuique can do a good amount of damage to the body.