Mac OS X - Mouse moves are not smooth nor constant I have a Logitech optical USB wheel mouse I've used for years on my PC (Windows 95, 98, XP, Vista, 7): http://www.clubic.com/shopping-1360-3-logitech-wheel-mouse-optical.html I'm now using it on a Mac mini with Mac OS X Snow Leopard (fully updated), but I have a problem with it. 

On my PC, when I move the mouse, the movement is smooth, and follow my hand moves. No matter if the move is large or small, the cursor goes exactly where I send it.

On my Mac, when I move the mouse, it seems to do what I want on large moves, but on little moves the cursor does not respond as well as on the PC. It seems to slow down, as if it had missed some move instructions, as if it was responding only one on two impulsions.

For example, when I try to catch the cross to close a window, I have no difficulties to reach the cross area, but to put the mouse exactly on it to close the window, it's as if I were moving the mouse on a badly responding surface. It's hard to reach the cross, like if the mouse was suddenly 2 times slower. Same problem to put the cursor beetween 2 letters on a text to make a precise selection, and other similar things. It's a nightmare!

I had tried many settings into the mouse control panel but it does not change anything on this problem.

I have also tried 3 other mouses, one wireless Logitech Mac OS compatible, one wired Microsoft and one wired Trust: all have the same problem.

What is happening? Do you know how may I solve this issue?
It seems like what you are referring to is not a problem with your mouse (as you've tried several). I'll also rule out the silly possibility that you are using all those mouses on a sub-optimal surface, like glass or uneven and rough wood, etc. I think you're simply experiencing the effect of different mouse acceleration algorithms between different operating systems.

As the physical hand/mouse movement cannot practically be mapped 1:1 to the cursor movement (you'd need a trackpad as big as the screen!), some kind of mapping algorithm between the hand movement and cursor movement is necessary. Mac by default implements it so that slow hand movement maps to a very slow cursor movement (for precise targeting), and a relatively fast hand movement maps to a very fast cursor movement (for moving quickly in a general direction but without fine-level accuracy). On Win machines a bit of this kind of acceleration also exists but it is not nearly as pronounced as it is in OS X. Some Win users switching to a Mac might find this maddening as their muscles and motor skills are used to something different. But same is true for a Mac user switching to Win. I.e. a Mac user might feel that mouse is traveling way to slow when reaching distant parts of the screen, and it's harder to do fine targeting in a small area. The Mac way does seem to work better the larger the displays are since it's benefits are more obvious in that case.

The good news is that if you just give it a week or two of constant usage, your muscles will likely get used to it and you won't perceive a problem at all. Based on your description, you might want to increase you mouse speed a bit though, to split the difference between big broad moves, and tiny, precise ones.

As a last resort, there are apps like Controller Mate:
http://www.orderedbytes.com/controllermate/help/?show=configaccel 
that let you adjust the acceleration algorithm used yourself.