Yeah this won't work for many reasons. And all of them have already been stated. I remember watching the gas prices last times this went around. They actually went down on the day of the we were not to buy gas. This caused a lot of people to go out and buy the gas. Then the next day the uped the price to stick it to the people that didn't buy ther gas the day before.
Also have you ever noticed that they aways schedule these on a Wednesday. Wednesdays are known to be the lowest gas selling day of the week. So they are not going to lose much money anyway. Plus this really won't effect a lot of people because not may fill up on Wednesdays. Now if you tried to hold this on like a Friday, Saturday, Sunday, or even a Monday, it might be more effective since those are the highest gas buying days of the week. But of course less people would join the cause.
Just to prove this won't help, I will be filling up my car tomorrow. Hey I shouldn't have to wait in line to fill up.