From what the Gamestop I was at told me there is no guarantee as to what system you will get (although they took my preference down and I was 1st in line) and there is no guarantee as to being "1st" or whatever.
Here is what I just was told and what happened while I was there:
I saw the email from corporate on the counter and read it while the guy was checking me out. My store is, as of the email, getting 16 units. They are taking preorders from 16 people. If they get 16 in, all preorders will get a system but it will be first come first served as to who get standard or premium. Also, if they only get 10 systems in, it will be first come first served among the preorders as to who gets those 10.
I think it is bullshit but don't really care because I will be up there at either midnight or when they open on the 17th.
Edit: Whether it is bullshit or not the guy at Gamestop also said Sony and Nintendo are trying to get or already have an agreement with EBAY to not allow PS3 or Wii systems to be sold on Ebay for 90 days after launch. I think that is bullshit but that is what he said.