Remember not to confuse bits and bytes. The theoretical maximum of USB2.0 is 480 megabits per second, which is 60 megabytes per second. Also, I believe USB2.0 is only half duplex, so it's actually 30 megabytes per second up and 30 megabytes per second down. That's before you factor in any overhead.
In practice, I generally find that most of the USB2.0 drives I have used tend to write at 4-15 megabytes per second, with cheaper ones being slower. With USB 3.0, I find that the drives I have tend to write at 60-120 megabytes per second. This can be a huge difference, especially as the price difference between USB2.0 and USB3.0 isn't that much anymore in my opinion.
A couple of weeks ago, I had to copy 20GB of data to a USB2.0 32GB drive my brother-in-law gave to put the data on, it took just over an hour and a half to complete. I then did the same to a USB3.0 32GB drive I had, and the same completed in just under 5 minutes. For me, that kind of time difference is well worth the extra expense and I simply don't buy USB2.0 drives anymore.
