I think the worst Apple product I've owned would be the Mighty Mouse. It's very difficult to use, the trackball is wild and spins all over the place, the wireless version is incredibly heavy, doesn't fit my hand properly, and worst of all: Only has one click, no separation between left/right clicking. This is something all Apple mice suffer from, and it's annoying. Some games and apps require clicking both left and right at the same time (for example, running in WoW, or performing tasks in Photoshop). So, to not be able to do that is a pain.
What about you?
What about you?