If you follow the link Pris posted to the MG website, there is a bit more information.
Their signings are usually numbered - the earlier purchases go first. I've not actually been to a release day party, but what they usually do is start assigning numbers the day of release - they do not take pre-orders. As a general rule, I call in near opening that day and purchase over the phone. Getting there earlier will help you get a good spot for the talk part of the signing, get your book in your hands, etc. I don't know that I'd camp out in store all day, though.
MG is an awesome store. They're very responsive to emails and phone calls and can probably help you with questions that I can't answer.
(I haven't been to the RB store much, but the original SD store is great.)