"You'll be hearing a lot about USB 3.0 this year. And well you
should, because its potential is vast. But will system vendors step
up to the plate to deliver all of USB 3's goodness?
"Speeds und feeds
"USB 2.0 has never delivered the advertised 480 mbits/sec
because that number technically correct and operationally bogus. If
you have data transferring in both directions at the same time it
could happen - but for USB disks it never does. That drops the
theoretical transfer rate to 240 mbits/sec, but because of protocol
overhead - for example, some signal redundancy to increase data
integrity - the payload bandwidth is still lower."