I've been to two VP launches, one for the iPhone 4s and one for the iPad2. They get very big. About 50 people will camp out over-night, and by the time the store opens the line is down around the Funny Bone near the theater. You will want to be there a minimum of 4-6 hours before open to get an iPad 2.
If you want a Verizon LTE iPad, the verizon store at 168th and center will have a shipment, and you'll only need to get there an hour or so early.
I pre-ordered my iPad, so I'm going to skip the launch festivities.