you are suffering from a small problem that happens with Ubuntu and some video cards. Not to worry. It also happened to me. It happens because there are some missed bugs between the relation of Unity/Compiz, the X.org system and the Video driver. This bugs of course are dealt with with newer, updated versions of Unit, Compiz, X or the video Driver.
The solution is to, when inside Unity and everything is slow and basically damaged, to go to TTY1, press CTRL+ALT+F1. When in the terminal, type your user and password to get to the prompt line. You can also get to the TTY when booting by pressing ESC or holding SHIFT, then on the GRUB menu, selecting recovery mode.
Now, there are several PPA I would recommend or other ways of doing this but to get to the point fast and have your system working do the following:
Install Xorg Edgers PPA
sudo add-apt-repository ppa:xorg-edgers/ppa sudo apt-get update
Depending on your video card you can either install the 304 series, 310 Series, 313 Series or any newer one that appears there. I recommend always test the latest version and only if it throws a problem, then go down from there until you reach a version where everything works correctly. For example, if you have a GT 9500 or later (Like in my case to which I also have a 440 GT, 560 TI and 680 GTX) the only version that solves all my problems is the 313.18 that came out a couple of days ago. So I would do this:
sudo apt-get install nvidia-313
This would install the latest version of the 313 series. It fixes MANY video problems with compiz, unity and xorg. The 310 series also fixes many issues but have not tested that one with my video cards. The other Nvidia versions are nvidia-experimental-304 and nvidia-experimental-310 as of this writing.
Reboot to test if your video card not works correctly with Ubuntu. If you happen to get any problems regarding Nvidia config file, simply open a terminal and type
sudo nvidia-xconfig and reboot.
There are other nice questions that could also help like:
How can I update my NVIDIA driver?
Newest Nvidia Card - what driver should I install?
Can't install GTX 680 drivers on 12.04
What's the difference between the nvidia-current, and nvidia-current-updates packages?
Or even one that is more generic: How to correctly enable Desktop Cube in Unity 3D?