Aside from aspects that have been covered on Gopherhole (agent % and whatnot), I don't know technical details, but it would seem to me that a boilerplate contract is likely to emerge that would address issues that would affect eligibility at the School.
So, if grades are required, schoolwork would become a job, a condition of the... grant? I don't know how to refer to it. Also, clauses that address poor behavior of one sort or another would seem to be a condition of payment.
Point is, the money might create more pressure to perform academically--unless you're at UNC, where there is no pressure.