So far, the only real uses of USB are peripherals, such as mice?, keyboards, and [digital camera]?s. There have been experiments that have monitors, hard drives, and networking components talking together, but these have not achieved general acceptence.
There are predictions that USB may replace PS/2 and AT style connections for mice and keyboards, but probably will not become a true "Universal Bus". Just like SCSI could have done everything, but turned out to excel at storage devices, USB may end up being used for a part of the interconnect on computers.
See also: Firewire