I would like to see everything on my computer screen in grayscale (like say the kindle screen). How do I do this?
Compiz has a few filters which supposedly can do what you want. Install Compiz Config Setting Manager from Ubuntu Software Center, run it and under Accessibility category you'll find Color Filter and Opacity, Brightness and Saturation filters. There you'll be able to enable them, assign a keyboard shortcut and edit the filters' settings.
Now, I have to admit that I wasn't able to test it since I only have Ubuntu in a virtual box without 3D acceleration, but hopfully it'll give you some pointers.
Also, please don't get too excited modifying Compiz settings - it is quite easy to break Unity by doing so. The filters I mentioned above should be quite safe though.