I used the wrong mouse for nearly an entire day.
There are a good number of computers in my office, but they all funnel through to two sets of mice, keyboards, and monitors. One set is connected to the machine I use for day-to-day activities; the other set is connected through a switch box to a collection of machines which I used for testing and a variety of other secondary purposes.
The switch box that controls the second set of mouse, keyboard and monitor makes no attempt to be smart, and if I move the mouse while it is connected to a computer that is broken into the kernel debugger, the switch box will often lose track of the mouse state, rendering it non-functional in all of the machines. To get the mouse to work in a particular machine, I have to reboot it. Since the machines are doing useful (although secondary) work, I don't want to reboot them. Whenever the mouse gets messed up like this, I just rely much more heavily on keyboard shortcuts, and when there's something that really needs a mouse, I fire up MouseKeys and use the numeric keypad to simulate a physical mouse.
One day, I spilled my drink on my desk, and I had to mop it up with some paper towels. And then after I cleaned up the mess, I found that the mouse didn't work. This didn't phase me much, since the mouse had a tendency to wonk out and I just went into my fallback mode of relying on the keyboard for getting stuff done. It's a bit more cumbersome, but it's not the end of the world.
It wasn't until near the end of the day that I realized that my mouse was just fine. It was a simple PEBKAC: I was using the wrong mouse.
There are three mice on my desk, even though there are only two mouse/keyboard/monitor sets. Originally, the mouse on the first set was a PS/2 mouse, but I later replaced it with a USB laser mouse since I was getting tired of cleaning the gunk off of the mouse ball. As a belt-and-suspenders sort of thing, I left the PS/2 mouse plugged in even though I didn't use it any more, figuring I could use it if this whole USB thing didn't pan out. Of course, the USB mouse works just fine, so the PS/2 mouse just sat on my desk, taking up space but otherwise not causing trouble.
Until I started using the PS/2 mouse thinking that it belonged to the second mouse/keyboard/monitor set. I didn't notice that the mouse was actually controlling the first computer because I wasn't looking at the first monitor when I used the PS/2 mouse; I was looking at the second monitor. And the cursor didn't move on the second monitor.
Once I realized what I was doing, I went ahead and unplugged the PS/2 mouse. The USB mouse on the first computer runs just fine.