It's interesting to read a couple of the comments from the Barcelona test:

Robert Kubica: "Of course we lose a lot of downforce compared to the 2008 car. But because we are back from grooved to slick tyres, we have substantially more grip in slow corners. So with some more development I don't think there will be too big a difference between the 2009 and 2008 cars."

Marc Gene: "We got rid of as many things as possible, to try to create the downforce we'll have the next season. But the main thing is the slicks. I couldn't directly compare them, but the first feeling is that the grip delivered by the new tyres compensates the lower downforce."

http://www.autosport.com/news/report.php/id/72177

The more things change, the more they stay the same