If you watch the keynote again, at the 1 hr 46 min point, you'll see a presentation slide showing that Quad-band HSDPA/HSUPA capability of the iPhone 4 is 7.2Mbps down and 5.8Mbps up. (The 3GS does up to 7.2Mbps down but only 384Kbps up.)
Obviously the AT&T 3G network doesn't upload at 5.8Mbps but I've seen up to 1682Kbps in my brief testing of the iPhone 4.
On Comcast cable via WiFi, I typically get 10Mbps uploads -- which is the same for both 3GS and iPhone 4.