What exactly constitutes a "Fair Share?"

I hear Obama demanding the 'rich' to pay their "fair share." I hear
Democrats and OWS scum (I'm being redundant, I know) claiming the rich
haven't paid their "fair share."

What is a "fair share?"

Is it 35% of your income? 50%? 99%? Give us a number and be done with
it. Or would that just nullify your whole campaign of class warfare?
In Obama's America, would anyone making over $150,000 entitled to
forfeit anything above and beyond? What is the incentive to exceed or
excel? Where is the reward for those that innovate and create?

Is it fair that some Americans are taxed at a higher rate than others?
Is it fair that some pay no income tax at all or actually receive money
from fellow Americans hard at work and paying taxes?

When will the OWS crowd pay anything at all or just go home and stop
burdening states with millions in police overtime, traffic snarls, and
cleanup-decontamination?