When I talk to a potential employer, I make a point of telling them that I work 40 hour weeks and I take a lot of time off. I've gone so far as to negotiate away my stock options in favor of extra paid holiday and the ability to take unpaid leave. Even when working for startups that think they're in crunch mode (and have been for the last 6 months), I make Life a priority.
Where I can, I try to spread the faith. Surprisingly, I've never experienced a case where I couldn't fix things and had to leave.
Stress is infectious. But so is Sanity. I've walked into shops where 60 hour weeks were the norm and managed to infect the team with the concept of Work/Life balance. First, you introduce the idea of "the weekend", where I'm living the back of my truck next to a crag someplace (and so should you), so don't try to contact me. Then you bring in "leave at six", then eventually "40 hour weeks". All the while keeping the rest of the team on board with the idea that maybe we should have lives apart from work.
Eventually, you have a whole team working 40 hour weeks and not looking so unhealthy. Some of whom even have stories to tell when you ask what they did for the weekend. Better still, if everybody is slacking off at a sane pace, there's really nothing that management can do about it (except notice how much more work is getting done).