I quit my last job on the spot without a new job lined up. Place wa horrible, my manager made me feel horrible -- even when they had spent the previous 7 months praising me, they still had a way of making you feel absolutely miserable -- and I got to a place where I had to leave or very bad things would happen. I've been with my current employer for about 2 years now and I love it here, love the people, the work, the company. It was very hard to walk away from a job without secured income but it was absolutely the right decision.
