All four ports are in use here in my (home) office: one to an old Pentium II workstation (with an archaic USB port I'd never tried out before), two to PIII-based laptops, and a fourth to a Mac Mini with a DVI output. My "head units" are a Kinesis Essential keyboard (with USB adaptor), a Kensington Technology Expert Mouse trackball, and a Samsung SyncMaster 205BW, which has a DVI input (direct from my Mac Mini) plus the usual VGA one. Aside from a shortish delay when switching the KVM between computers, it works great, and doesn't seem to require a display connection for the USB cables and switching to work, which is something I'd worried about. When I switch to the Mac Mini, the Samsung detects lack of VGA signal and automatically switches to the DVI input; going in the other direction, I simply press one of the buttons on the monitor to tell it to switch back to VGA. One of the laptops (running Fedora Core 6) gets along great with the Samsung's config, but only once I configured the BIOS to use "CRT only", not both LCD and CRT. (I tried fiddling with X's config a bit, no joy, I'm not an expert at that though.) I'll try that with the other (running FC3) later; in the meantime, the Samsung alerts me that the config would work better if changed when I switch to the FC3 laptop; pressing "Menu" dismisses the alert.