I'll never do a midnight launch again, only because it sucks investing the time in waiting to get the system, only to bring the system home and be fatigued and sleep.
For the 360 launch, me and some friends went to Walmart 14 hours before midnight and were 7th and 8th in line respectively. They stashed us back by layaway so we were out of the way of customers. Just lots of waiting on the hard floor, trying to pass the time. The staff was pretty cool about it, and the store manager brought us cookies and bottled water. It went much smoother than the Wii launch. We underestimated the demand for a Wii and the Walmarts we checked out were packed beyond the supply. We ended up going to Target. Since they're not open 24 hours, we had to wait outside in the cold until the store opened the next morning. We had people trying to cut into line in the morning, and the staff only came out an hour prior to opening to assign numbers.
What I'm getting at is, depending on where you live, if weather is an issue, invest the extra time to find a store that will let you wait inside until midnight.