I have a question. How important are meta tags for SEO?

<meta name="description" content="Your description here!" />
<meta name="keywords" content="your, keywords, here" />

I've read conflicting reports. Some people swear by them and others say not to bother as it doesn't really help. I'd just like some input from the members here. Perhaps you've had a site that didn't use them and ranked at a certain level but then had a ranking that improved after adding them (or not).

Does anyone have any experience with this?