Unity won't load with proprietary drivers

First time running Ubuntu 11.04 and getting used to Unity, I decided to install proprietary drivers for my Nvidia graphic card.

The output of lspci | grep VGA is:

00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: nVidia Corporation Device 0df5 (rev a1)

If I activate the driver that is "recommended", next time I try to login in a Unity session it just changes to the classic. How can that be happening?

I attach the screenshoot of my proprietary driver screen:

Have a look at the bumblebee section in https://launchpad.net/~hybrid-graphics-linux

b) try bumblebee for simultaneously using the intel and nvidia cards:
sudo apt-get install git
# type password
git clone http://github.com/MrMEEE/bumblebee.git
cd bumblebee/
sudo ./install.sh
optirun glxgears

# check the speed and compare to running:
glxgears
# If you have google-chrome installed, you can try it with/without optirun and report the FPS values on the mailing list:
optirun google-chrome http://webglsamples.googlecode.com/hg/aquarium/aquarium.html