Logitech Control Centre Software is awful. Not only do Logitech not support their G400 under OSX, they make it hard to find this out. But the software installer is a heaped on insult:
You tun the installer for Logitech Control Center (LCC) having downloaded the latest version from the Logitech Website.
The installer prompts you to update to the latest version of LCC
You realise after some Googling that LCC doesn't support the G400 on OSX
You can't run the installer to remove the software because it says a newer version of LCC is already installed
You as a user vow never to buy Logitech products again. Even though you know you will as you don't like the Apple Magic Mouse and never really liked Microsoft Mouses either so what choice do you have?
But here's a solution to get the G400 supported under OSX Lion:
Download and Install SteerMouse
In the Terminal paste:
defaults write jp.plentycom.SteerMouse LOGITECH_G400_PLUS_MINUS -bool YES
Instant insane cursor speed!
Open the SteerMouse Control Panel from System Preferences and adjust as required.
It also supports the G500 and G700 as well and probably others.
Interestingly the G500 has an onboard memory that holds the configuration, so apparently you can configure the G500 under Windows and it will remember the settings when used in OSX. I haven't tested that, but you could configure a G500 in a VM if you are using a Mac.