The Apple Mac OS mouse cursor speed is one of those “love it, or hate it” domains. Personally I find the default speed already way too slow, always falling asleep on a fresh Mac install, or at the login window.
The max used to be barely endurable, so far, e.g. with the Mighty Mouse - until I got the Magic Mouse the other day. Directly compared the Magic Mouse moves way slower with at the same setting. No idea how Apple got this inconsistency in their own, few products. I also have no idea why mouse pointer movements can possibly be that slow. Not only the default, but also the maximal configuration value, …
Fortunately there is no limit behind the back, so you can tune it with:
defaults write -g com.apple.mouse.scaling -float 8
The 10.6.2 maximal UI value appears to be 3, …
Update: Some more review: The slowness aside, the Magic Mouse is pretty decent. The biggest improvement over the Mighty Mouse is the touch sensitive cover. The former microscopic scroll ball was prone to accumulate dirt inside and near to impossible to clean. (To really clean and remove dust and dirt from the ball axes one hat to cut(!!!) the glued mouse housing and disassemble it fully, …). So from this usability standpoint it’s a great improvement. The major downside is, that only a Bluetooth version is available. I personally find the weight of the two AA batteries too hefty - that was also already a problem with the Bluetooth Mighty Mouse. For my excessive workdays I would prefer a lighter, cabled version to reduce the wrist stress, …