I recently bought a Belkin USB hub (self-powered) and have used it to plug in the iPod connection cable, digital camera cable and the keyboard. On the other two USB I have an external harddisk and a wireless Logitech mouse. Whenever I booted the iMac it would start up just fine and then after 10 or so minutes become extremly sluggish, the mouse jumping constantly to the corner, not being able to click, the dock wouldn't animate, etc. It took me a while, but eventually I noticed that as soon as I disconnected the hub it worked just fine. But I'm wondering, is it likely a faulty USB hub? Or is it normal to slow down my system so much? I'm a switcher and my PC had 8 or so slots, so I figured a hub would be a good solution.