Pulled from gtaforums since I don't know how to word it.
Basically my gta fucks up if I don't have my mouse plugged in. When it's plugged in it works fine but without it eventually it goes wacky. Things like exiting a vehicle automatically makes the camera pan to the right, the original scrolling buttons (4 + R) are changed so now instead of scrolling up and down with radio stations and weapons, you can only scroll in one direction and the other key doesn't work at all.
I can't describe it but it's annoying and I don't want my mouse to be plugged in all the time. The touchpad is good enough.