You might not feel like you owe anything to your employer who has cut back on benefits and maybe even pay, but any deficits on their part don't justify get-up-and-go behavior when you find something better. MSNBC interviewed one CEO who is shocked by the number of employees who are dashing out without giving the customary two weeks notice. His company went through a round of layoffs, and he suspects the uneasiness of those employees left on payroll has contributed to their behavior.
Even if you're fed up and want to hand in your security card as soon as possible, it's important to leave on a good note. Giving your employer notice could mean the difference between using your old boss as a future reference and having to dig up other connections. And if your sudden absence would leave co-workers picking up the slack, you couldn't exactly expect them to have your back if you needed to network down the road. Giving appropriate notice is just one of the steps for leaving your job gracefully, but it's an important one.