I have toyed with the idea of getting rid of the exhaustion table, and replacing it with a cumulative -1 to all rolls (ability checks, attack rolls and saving throws), -(level) to max HP, and -5 ft to movement per level of exhaustion. This makes the progression much 'smoother' and would prevent me from having to remember a table.
However, it woudn't make much of a difference since exhaustion comes up so rarely. I like the ideas presented in this thread, especially the idea of recovering abilities by taking a level of exhaustion. Does anyone have a version of this written up somewhere for the different classes?