Preordering from Gamestop to get bonuses

[Buffalobiian]

The main impetus for this thread is Dead Space 2. I've got 5 days to decide whether or not to pre-order to get the rivet gun and mini-game. I think it's like Dead Rising Case Zero where it's a few playable levels and any character attributes you earn carry into the full game.

Does it cost extra, or is it cheaper to preorder?
Will you get the game regardless (unless it's utter crap)?
Will you get the game relatively soon, or in months time when it will likely be on special?