I tried USB (my current mouse is a usb with an adaptor to ps/2) and found that the response was a lot slower.
Since I'm a SCSI addict, so giving up two interrupts to my primary means of interfacing with the computer doesn't have huge evil ramifications for me.
USB is very good for some stuff; the new MSD drivers coming out for OS/2 mean that mass storage devices like cameras, thumb drives, etc, are all working quite nicely, and for those sorts of things USB is an excellent interface. Now if only we could get some good firewire stuff happening ....