Hmm interesting. Most of these sites require that the app was Paid before? They usually say it must have been paid for at least 1 week before the promotion.
I think at least, if not more than, 50% of the downloads you receive are due to trackers tweeting and posting about a price change. Thats why they have that requirement, and the ‘week’ is to make sure all of them update 
I would be interested in the result you have, but I have a feeling you’ll top out at 20 to 30k if you’re lucky.
Have a read of this to see what you could expect WITH a price drop being tracked by all these other sites:
http://www.mindjuice.net/2010/12/10/game-giveaway-the-numbers-post/
Also look at app shopper:
http://appshopper.com/
They track the drops and have a RSS feed alot of other sites use to twitter to their followers.
Its not as easy as you think, or EVERY free app would be promoting like this
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