As far as we know, effective rate reaches at 40MBps or 320Mbps for bulk transfer on a USB 2.0 hard drive with no one else is sharing the bus.
Flash Drives seem to be catching up too with the some hitting 30MB/s milestone. For all we know, manufacturers may claim USB interface becoming the performance bottleneck for flash drives as early as 2007. Additional notes from Alex Esquenet - our engineer friend based in Belgium:
"A fast usb host can achieve 40 MBytes/sec. The theorical 60 MB/sec cannot be achieved, because of the margin taken between the sof's (125 us), so if a packet cannot take place before the sof, the packet will be rescheduled after the next sof. On top of that, all the USB transactions are handled by software on the PC. For instance, a USB host on a PCI bus will send or receive the data via the PCI bus; the stack will prepare the next data in memory and receive interrupt from the host."