This is the officiaL U.S.State Department website regarding the duration and extensions of stays:

http://travel.state.gov/visa/temp/info/info_1298.html

For information on visas, see specifically:
http://travel.state.gov/visa/temp/in...1298.html#Visa

For information the I-94, see specifically

http://travel.state.gov/visa/temp/in....html#Duration
- point 5.


"The date or D/S notation, shown on your Arrival-Departure Record, I-94 or I-94W is the official record of the your authorized length of stay in the U.S. You cannot use the visa expiration date in determining or referring to your permitted length of stay in the U.S"

There you go...straight from the horse's mouth.