My experience has been like saidso. Some places seem to care about references, others not at all. It varies a lot.

And, I also agree with divine that it could be a co-worker. I quit my job before my current one. The owner had anger management issues and did not take it well, so he was out as a reference. However, the editor/journalist I worked with closely said she'd happily be a reference for me. It was clear she knew he'd never provide a decent reference, even though I was polite about everything and gave two week's notice, etc.