Dark Void's pre-order bonus item seems like it drastically changes the gameplay more than any other bonus in recent memory.
Pre-order bonus items are sometimes pure vanity - Gears of War 2's golden Hammerburst comes to mind - and sometimes they actually do change the way the game in question is played. Dark Void's pre-order bonus item deal with GameStop seems to actually be something of both, and possibly quite a bit of the latter.
When you plunk down a deposit for Dark Void at GameStop, you'll earn access to a golden jetpack which not only looks cool (though I think it's a tad garish), but also grants you unlimited boost in-game. While we're not completely clear on the specifics here, if we take the word of the advertising, this item gives you "unlimited turbo boost and special moves" and makes you an " unstoppable master of the skies."
Maybe there will be some kind of limit to how unlimited it is, but if there's not, essentially with this item in tow, you'll have infinite resources in Dark Void. No limits on turbo, no limits on "barrel rolls, quick 180s and more." For a game where you're rocketeering around quite a bit, I imagine that unlimited turbo would make the experience a bit more of a breeze than it would normally be. Oh well. You can always just not use it.
For what sounds like such a game-changer of a pre-order item, Capcom and GameStop have put together a bit more promotion than publishers usually do for these kinds of things. There's a fairly ridiculous website and an equally ridiculous commercial, that I'm guessing is supposed to be a parody of crummy late night infomercials? According to the promo, the gold jetpack will give you "more boost than my step-sister's push-up bra." I don't know about the pre-order bonus, but when it comes to comedy, we call that gold.