11.10 has been a bit of a mixed bag. On the plus side it has Gnome 3, giving me a practical (and in my opinion superior) alternative to Unity. On the minus side I had upgrade glitches on both my work and personal machines, and they were unrelated issues! Might be wise to wipe and reinstall for this one (you did separate your home partition when you installed didn’t you :)).
Anyway after getting it working on my work PC (which has an 8400GS), the desktop was quite laggy in both Unity and Gnome3. It was still usable but I didn’t realise how bad it was until I went home and noticed how much smoother my laptop was, with its lowly 2009-era Intel integrated graphics…
The solution was to install the latest 285.05 Nvidia driver, but trust me when I tell you that you do not want the hassle of using the Nvidia installer from the Nvidia website.
It is much simpler to use the X Updates ppa.
So assuming you already have the default binary Nvidia driver installed and activated (nvidia-current), the quick command line solution to your performance woes should hopefully be:
sudo -i add-apt-repository ppa:ubuntu-x-swat/x-updates apt-get update && apt-get upgrade reboot
You should notice an update for the nvidia-current package being installed.
That wasn’t too bad was it? :)