There is no simple way to disable the workspace switcher. It requires changes in the code of Unity 2D.

I'm running Ubuntu Precise, and the following did it for me:

• Run "CompizConfig Settings Manager" (not sure if it's installed by default)
• Select "Desktop Wall" under Desktop
• Disable "Show Viewport Switcher Preview"
• Select the "Viewport Switching" tab
• Set "Wall Sliding Duration" to zero

Now when switching desktops via the keyboard, I don't get any animations.

Install dconf-tools (should be available in Maverick, it definitely is in Natty. I'm on Lucid so I can't check). Open dconf-editor and search for unity. There are several tunables, though I'm not sure the workspace animation is one of them.

Probably the best solution is to log in with the "Classic Gnome Desktop" (drop-down menu is at the bottom of the GDM Greeter after selecting your username). This will avoid Unity completely.