Sales could double, since there's more than a price cut to be looked at. Fact of the matter is, there haven't been many games to justify a PS3 purchase regardless of price. Once the games start to come, the system will sell more. The fact that it's being paired up with a price cut is just gravy.
Now, there's no way in hell sales are going to double off of the price cut alone. That's asking too much of too little. But the fact of the matter is that this cut might push MS to cut sooner than they planned while a good Fall line-up wouldn't have done the same. People see this number and pay more attention to it, even if the initial cost of the console isn't the biggest reason behind its success (or lack there of, in the PS3's case)
You do not have the right to never be offended.
