Avoiding Burn-out - What's Your Advice?

The pay is low.
The hours are long.
You're almost guaranteed to catch the "cold of century" every year.
We welcome new people to the profession every year and we see almost as many leave it every year citing "burn-out."
Also every year we celebrate the folks who have made it ten, twenty, thirty, or more years in the classroom. You're the people we want to hear from. What's your advice for avoiding burn-out as a teacher?