Mouse speed inconsistent

I know exactly what you are talking about - This is a "problem" with Mac OS X - Leopard and Snow Leopard at minimum.
Many people don't have a problem with it or dosn't even notice it, but especially us who comes from the Windows world have a lot of problems adapting to the mouse handling in OS X.

There is no way you can turn on directly in OS X, which is also why quite a lot of people have been complaining about this for years, but Apple still refuse to give us the option to turn acceleration complete off so we can get a straight liniear mouse.

You do have a few options to "fix" this though - You can't fix it 100% but there are some ways to get almost normal mousemovement.

1. You can purchase a program such as Steermouse or USB Overdrive which lets you change the settings of the mouse a whole lot more and which gives you the option to disable acceleration. I've been using Steermouse for two years with success. The only problem is that when you disable acceleration the mouse is very slow, which means you have to increase sensitivty which makes the mouse somewhat more unprecise(Only noticeable for VERY small movements(1-2 mm)).

2. If you have a Logitech mouse, you can install the Logitech Control Center driver from Logitech's website, which will give you nice linear movement. I've heard people say the same about Microsofts driver and their mice.

3. In the Terminal you can use the following command to more or less disable acceleration: defaults write .GlobalPreferences com.apple.mouse.scaling -1
Some people claim that this will slow the mouse waaay down, but I haven't experienced it - If you do you can either try to increase the speed in the system preferences before you execute the above command in the terminal or you can disable it by just setting it to 1 instead of -1

4. Live with it - I know how hard this is...Trust me, I've been trying for years without luck although I will admit the more you force yourself to use it the more you accept it. ButI still believe that Apple should give us some better mouse options - Especially for all the switchers.

It doesn't ring a bell with me. I have heard that mouse drivers don't track movements linearly, so some acceleration is normal. But what you describe sounds very extreme. Do you have any other mice you can try, to compare?

I don't believe that what you are experiencing is normal. I switch back and forth between XP and the Mac and don't notice a significant difference in mouse behavior. If you try another mouse then you can tell if the trouble is in the computer or the mouse.

What kind of mouse to you have? Are there special drivers installed for it?

You could try to fiddle with the settings in the Mouse system preference. They may be out of whack. If that doesn't fix it, check the web for Mac drivers for your model mouse and install them.