At my local Target there were 3 people lined up at 4 AM, but less than a dozen by 6:00; the rumor was that there were 47 Wiis.
The line really started growing at 6:30, and someone in the line worked at this Target and said there were 71 Wiis. Someone from inside the store told the line that tickets would be handed out at 7:00 but that no one could leave the line between then and 8:00 when the store opened.
As it turned out, there were in fact 76 Wiis, and the tickets weren't handed out until 7:40. Anyone who desperately needed a 15-minute break was allowed to leave, but Target Guy warned that people not in line by the time everyone went inside would forfeit their places in line. I don't think anyone missed the deadline.
As it turned out, everyone in line at 7:40 got a Wii, with 5 left over that lasted about 5 more minutes. I was surprised -- I thought they would run out between 7:00 and 7:30.
Basically, anyone who showed up at all early got one.