I think there is a lot of speculation in this thread. My friend got Halo 3 on the Saturday before it was released, played online and everything. He was never banned in any case. Nothing happened. All that happened was that the achievements didn't tally the time until the game was officially released.
He actually played against people who bought it at the same place online, no one got banned. Maybe a few got banned, but you're over speculating.
Personally, I'm likely to get it on Monday (I could get it Sunday if I want), I'm not sure I'll go online, but I will be playing it all day Monday. I guess that adds to my e-credit.