You were going to preorder it regardless anyway, right?
Were you hoping to be able to spend some time with Modern Warfare 2 before the November 10 launch date? Unless you can find a retailer who has broken street date, you're not going to get any time with the upcoming modern warfare shooter until the intended date.
The official Infinity Ward Twitter replied to a user asking about a demo, saying, "No plan for a Demo before launch. The entire team is focused on polish all the way up to ship of the full game."
Of course, with the success of the original Call of Duty 4: Modern Warfare, there really isn't a whole lot of marketing rationale in spending time to make a demo for a title that will surely break some sort of sales record for the 2009.
While those anxious to try the game ASAP will be disappointed, a more focussed and less stressed development team mean a better product. Besides, you need all the time you can get to save for you pennies for the Prestige Edition with night vision goggles.