Tiny
You might get away with it ONCE, till they found you, but I think they would be very reluctant to let you back in the country again if you did.
Besides which I dont know if you realise but if you stay for more than 180 days in 3 years (using a formula they have which is so many percent of current year + percentage of 2 previous years, then all your worldwide income is subject to US taxation.
People have been refused entry for overstaying on Visa and visa waiver by just a few minutes over their allotted time in the not too distant past.