I understand that the I-94 (green form) is now gone away..and so you have no choice but to complete the online form 72 hours before you go...they say, that if you have not completed it, they will either detain you, or send you straight back home!
The on line form takes about 4 minutes to do, and the approval takes seconds..assuming you haven't ticked the "yes I am a terrorist" box!..then lasts 2 years...just need to update it if you have a different US address each time.
I doubt it wil speed up immigration a huge amount..as they will still have to find your visa approval on their system, whilst you stand there.
TW