revial: The mouse is software emulated instead of hardware.

Which means the more load your system is under, the higher the chance it will suffer from that "lag".

While there are some things you can do to help to decrease the load, ultimately the only real fix is for them to implement hardware mouse.

It isn't an issue I've heard them talk about, so I have no idea if it's on their radar for an upcoming patch.

hanns.g: You might find the mouse a little more responsive with a few tweaks.

Make sure Ubersampling is off.

and/or

Disable Vsync

and/or

Editing C/documents/Witcher2/Config/User

[Mouse Input]
Smoothness=0

Different people get different satisfaction from these tweaks, depending on systems and perception. I don't think anyone will be truly happy 'till hardware mouse is implemented.

What really saved me was just going to arrow keys and keyboard to navigate menus, primarily.

As far as combat commands, I find the space bar to be especially unresponsive. The other keys, I mostly chalk up to action queing. I eventually got used to that. I wouldn't complain if it could be adjusted though.