This isn't a problem with the Mighty Mouse itself (though I'll be the first to admit it is an awful mouse); this is to do with how OS X handles mouse movement. If you've recently come from Windows or if you change between the two (or even Linux) you will notice that OS X mouse movement seems to "stutter" at slow speeds and then accelerate very quickly after that, therefore giving the impression of lack of precision. You'll get used to it. You might even notice this if you're coming from using an Apple trackpad, as the feature/problem isn't nearly as noticable.