I get empty boxes instead of characters in Emacs. Why?
By default, Emacs uses a font called “default”. This should be a system-wide alias for some sensible default font. Ubuntu, particularly, has no such alias. Consequently, Emacs displays a boxes instead of characters. You can fix this by changing the font Emacs uses (see previous question), or by using antialiased fonts (see next question). Possibly you can also fix this by adding a default alias to the font subsystem; I don’t know how to do that.