I started using Ubuntu and didn't really like how fast the mouse moved, so I found out the command to change it
xinput --set-prop 11 "Device Accel Constant Deceleration" 4
Which will make it slow, but it's annoying having to type that in every time. I made a normal new gedit file "mouse_sensitivity" in my ~/Documents folder, and in /etc/rc.local I put:
Obviously, my problem is that this doesn't do anything when I restart my computer.
Quick note about the command I'm trying to use. It works and everything in the terminal or when I execute /etc/rc.local. If anyone else was looking for that command, beware that '11' is the associated number for my mouse, but probably not yours. And '4' is a really really slow speed for a pointer, but I just wanted to be sure that I'd notice the difference.
Also, I haven't edited it but when I execute /etc/init.d/rc.local it doesn't work. I can get those errors for you if you need.