To date, the only time I've camped out overnight for something was for the Wii launch. It was on a sunday morning and I didn't have anything better to do that weekend so I said "what the hell". Wal-Mart was having a midnight launch, so I went to one that I figured would be the least crowded and found a line of about 20 people. This was maybe 8:30PM.
At 10PM there was maybe 50 people in line at this point, and a manager came out and said, "We have 20 Wiis available. Work it out yourselves," and went back inside. No line tickets or anything, very unprofessional. After the anger subsided, we eventually organized ourselves to count off and figure out where the cutoff was. Of course I was #21. I maybe had a chance, but didn't really feel like chancing it.
On the way home I stopped by Best Buy to see the massive line. To my surprise there was only about 40 people in line, and they were pretty excited, saying there was a good chance there'd be at least 100 Wiis available. No midnight launch, but there was a good chance I could get one. I went home, got some warm clothing and a camp chair and came back, and was about #50. The Best Buy even stayed open until midnight, and after closing many of the employees themselves got in line for the night. Mad Mario Kart action was had by all. By morning there about 80 people, we got line tickets at 6AM, and they announced that they had over 150 units available. The store opened at 8AM and I got my Wii.
(Frankly, had I known they would have supply problems for years after that, I would have bought 10 of them. Oh well.)