Currently when a module is included into a classes, it is appended to the class hierarchy (ie. the method lookup order). This of course makes sense, but there are times when it would be useful to prepend the module. For example:
def x; "x"; end
def x; '[' + super + ']'; end
C.new.x #=> "[x]"
One big advantage of this is being able to override methods in a safer way, rather than using alias or tricks like alias_method_chain.