Money buys freedom. Save up a couple years of living expenses and you can go do what you want for a couple years. If you're prudent, this could also develop the skills that'll make sure your next job is both more fun and more lucrative than your past ones.

Actually, you don't even have to quit. Just knowing that you can quit, if you're not happy, changes how you interact with your employer. Don't like what you're doing? Do something else, either there or at a different company.