Interesting. Wild guess - I expect the iPhone 4 to score about 400. Maybe even 500. My 3 year old Macbook 2.2ghz scores around 2600.
400-500 is a decent score for something that's 1/4 of the size and weight of just my macbook battery. The way things are going, iPhones will be as powerful as laptops in 5 or 6 years time.
Benchmarking a phone. Huh. 3 years ago I would have laughed at the idea.
Considering 3GS is ~260 give or take, I'd not expect it to jump that high. Though, if the memory performance is as increased as rumoured, I guess it just might.