According to TreeHugger, Toyota has over 20,000 pre-orders for the 2010 Prius, a number which should reach 40,000 by the time the cars hit the dealerships.
In 2008, Toyota sold 73,100 previous-generation Prius hybrids, so the claim of reaching 40,000 pre-orders before the car is even available is pretty impressive (especially in this economy).
The price might also go down partially in response to the new Honda Insight
In Japan, the new Prius is expected to be less expensive than the previous model (2.05 million yen, or about $20,750), no doubt to better compete against the Honda Insight. We'll have to wait for pricing information in the rest of the world, but I wouldn't be surprised if they managed to reduce the price; a lot of the changes that were made to the hybrid synergy drive (HSD, what Toyota calls its hybrid drivetrain technology) had for goal to make it smaller, lighter, and less expensive.
Personally I'm less than thrilled with the 2010 Prius. It will have a solar roof among some cool features and get 50 mpg (about 25% better than the Insight), but I'm still waiting for Toyota to at least make a plug-in version of the car. Still, good to see them selling well already.