If they drop the price $100 dollars they will seem desperate as they already had a 'price drop' this year. Everyone informed knows the first price drop was a bit of a sham (They dropped the 60GB down to the 20GB price, it was more of a feature increase than a price drop as such.) but everyone who isnt informed will think that Sony has desperately dropped $200 dollars off their console. That isnt good for consumer confidence.
Meh, I think it would be better for Sony to wait until early next year to drop the price, by then everybody will have forgotten about the last 'price drop' anyway.
@Sorrow, you are right it will greatly increase sales for a period of time. Each segment of the market has a certain saturation with the release of a $400 console Sony will be accesing a market segment that the havent currently targeted, but eventually that market will become saturated. What I'm trying to say is I dont think that overall their console sales will increase by much if they drop the price now as compared to next year as the same market segment of people willing to pay $400 for a PS3 will still, mostly (some will have bought a X360 instead), be there.
The increase in sales as such wont be permanent as they will have to drop the price again once that market is saturated. The Wii currently seems to be running in to saturation problems in Japan.