Okay, two follow-up questions:
Generally speaking, what's the lowest price for a pre-order on a typical $50 retail game?
And, roughly, when is the best time to pull the trigger on a pre-order? Right when the game is first announced (i.e. 9 months before release)? Three months out? etc.
Best time to pick up a pre-order
is when you find it somewhere for under $40. Generally speaking, that doesn't happen with every game (especially from companies like Activision), and you're not going to find it any lower. For example, Borderlands 2 was available for about $36 through a really good Amazon promotion. I don't think that has a lot to do with timing, you just have to keep your eyes open for the best promotion/price.
That said, pre-orders are only good if they come with bonuses that you're really interested in. Otherwise, if you can wait a year, you can easily get the game for 50% off or more (and obviously it doesn't always take that long; look at Spec Ops and Max Payne 3). Only pre-order games that you MUST play now; otherwise waiting will save you a lot of money.