After running around Middle Earth in Lord of the Rings Online for a while, I think I've narrowed down the nature of the mouse problem in the game. I use a Naga Razer mouse that has settings for mouse cursor sensitivity and how many times to poll the machine per second. It seems to work better at extreme sensitivity of around 5500 and low polling frequency of 125 times per second. The acceleration was down to 2 although I've tested it at zero. Basically the nature of the problem is the extreme inertial behavior of the mouse control especially as keeping both left and right buttons pressed down for forward movement and moving the mouse left or right to turn the character's direction and up or down to control the viewpoint from over the character's shoulder up or down.
What happens is that when the character is turned while moving, one can't turn in the other direction right away. Moving the mouse left after having moved it to the right will keep my character moving to the right for a couple of seconds before it moves in the other direction almost like sort of an inertial resistance to any change in direction. Whether it's from right to left or left to right or up to down or down to up seems to make no difference in the inertial lag.
With the Razer Naga gaming mouse I was using, I have found that keeping the polling rate very low, the acceleration low, and the sensitivity extremely high improved the inertial problem with the mouse, but didn't negate it altogether.
