A noticeable amount of  Ubuntu Users seem to complain that Ubuntu 11.10 is slow, because of the Unity Ubuntu 3D theme. Ubuntu also has a Ubuntu 2D Unity theme which has fewer animation, and work better on slower computers.
Making Ubuntu faster by using a more basic theme and by adjusting desktop settings will make Ubuntu use less power (better battery life for laptops and mobile computers) , and allow you to run more demanding programs on your computer with less slowdown. A faster computer will also improve your productivity since you can get more done, and not be slowed down by slow PC performance.
All you have to do is click on the settings button next to the password box and pick Ubuntu 2D instead of Ubuntu 3D during login then type in your password, and login. I also heard replacing the desktop with a solid color, and using a more basic looking theme like the default grey theme from Ubuntu 9.10 and older can make your computer use less RAM and CPU cycles, but it might not be noticeable to humans.
Changing the desktop environment may not make programs launch faster, but it will improve the performance when running more then one application at the same time, make your file server be able to stream to more devices at once, or playing higher quality 3D games since more free CPU and RAM are available.
You can also use the Ubuntu Software Center in Ubuntu 11.10 to search for and install the LXDE, or XFCE theme which are light weight themes which are designed to work better on slower computers compared to Unity, KDE or Gnome themes.
In LXDE there is a “Desktop Session Settings” Program where you can find in the Preferences menu in the LXDE menu on the bottom left of your desktop. The “Desktop Session Settings” has a tab labelled Automatically Started Applications where you can uncheck the programs which you do not need. I found it safe to uncheck most of the programs on the list except for PulseAudio Sound System which is needed for sound.
After you unchecked some of the startup programs for LXDE, your computer might be slightly faster since less startup programs are running in the background. It is also good to keep track of what you unchecked just in case you need the program to start up automatically by re-checking it.
The one main disadvantage of LXDE and XFCE theme is they both are not as user friendly as Gnome and KDE, but if you used Windows Operating System or Mac OS before, learning how to use LXDE and XFCE is very easy.
To switch your theme to LXDE or XFCE when installed in Ubuntu via the Ubuntu Software Center, log out, and click on the Gears setup Icon, and pick LXDE or XFCE when installed, and when you are log-in to your account in Ubuntu, you will be either be using the LXDE or XFCE theme depending on which one you pick.
You can also use LXDE and Ubuntu by installing Lubuntu 11.10 on your computer which uses the LXDE theme as it’s default theme.
XFCE version of Ubuntu is Xubuntu which use XFCE as its default theme.
In my experience the LXDE theme is faster then the XFCE theme when running in Ubuntu, but XFCE seems a little more user friendly and attractive to use then LXDE which is a very plain user interface compared to other Ubuntu desktop environments.
Other tips for making Ubuntu Faster.
Make sure all your hardware is compatible with Linux, and met the system performance requirements for Ubuntu.
A multi-core CPU like a dual core CPU will make Ubuntu Linux faster as well, and installing 1GB of RAM or more will improve the speed of intensive tasks like High Quality gaming. A video card will also make Ubuntu faster when gaming. I read online Nvidia video cards are generally better for Linux then ATI.
Also make sure your computer is in good condition meaning all the parts are working, and not failing since a failing hard drive, motherboard, power supply, RAM, or overheating CPU and video card can make your computer unstable and slow.
Keep Ubuntu updated which is not hard since I think Ubuntu installs updates automatically for the operating system and most software installed in 11.10, but you can still check for, and install updates manually.