It is sad that teachers are considered to be underpaid. If a teacher truly cares about his or her students and works hard to help them be successful, they should be paid for that. If a billionaire wants to use his or her money to reward teachers for a job well-done, that is their choice.
The incredibly wealthy are so much better off than the rest of us I'm surprised they can sleep at night without wanting to help fellow humans. The amount of money it would take to raise someone out of poverty is just a drop in the bucket to these people. Why they feel the need to continue to hoard it is beyond me.
I think philanthropists should be able to step in and help in multiple situations. Those whom are better off economically should support people and causes that need their surplus in money. It is also beneficial for those donating for tax reduction purposes. Private philanthropists should be able to step in when state employees are underpaid if that is an issue they feel strongly about. Philanthropists, for that matter, should be able to help any cause they see fit.
Hedge's donation is a nice gesture, but I think that it solves the problem only temporarily. By donating the money to underpaid teachers he also solved the problem for the people who should actually pay them. And they can't get away with not paying well the teachers forever, because there won't always be private philanthropists to do their job.