Get there before the others do!
Of course, I would imagine that not all the population of Nome, Alaska, will be queueing up to buy an iPhone4 so if you get there around 6:59am, you should be fine.
Think about your question and then make your own decision based on where you live and what you perceive the demand for an iPhone4 to be in your area.
Right now, you are the only one who knows where you are!!!
I was one of the unlucky ones who couldn't preorder the iPhone 4 on the 15th, and will be waiting in line at my local AT&T store on the 24th. But: when should I get there? The doors open at 7 am.