Be careful Karma, I believe you mean 480Mb not mB and you are right, it is 480 Mbps vs the ESATA of 3.2 Gbps (or 400MBps). Even with that said, the actual transfer rate that most ppl experience on a USB is about 22 to 25 MB (MegaBytes). Firewire is going to rise to about 6.4 Gbps eventually and eventually ESATA will rise to about 6 Gbps however right now, you are are looking at 480 Mbps (USB) vs 3.2 Gbps (ESATA).
EDIT* That is the theoretical speed, I suppose any number of factors could make it transfer at slower speeds.
EDIT* sorry for the second edit, I want to add something else. Just to say, why the theoretical transfer rate of a USB is 480Mb but it only generally transfers about 22 to 25 MBps. Even though it is rated at 480 Mbps, the USB protocol has quite a bit of overhead. Essentially, you are not just sending the data you want to send but also a lot of the preprogrammed data that that Indian dude on the intel commercial invented!!! It helps it get to where you want and unravel itself into something the other computer can understand.