My idea for a W4: Enter the % you want withheld (min 8%). You can still claim exempt if you expect your EIC or other credits to zero out your tax.
This will help part-timers, especially if their hours vary and sometimes have no tax withheld due to low hours in a pay period.
Then everyone will be having a discussion about what % they're having withheld and people will start to understand what their effective tax rate is. And if they're under/over withheld, they can easily increase/decrease the %.