I think bounce rate is one factor google uses to determine how much traffic to send you. I worry because my bounce rate is high. But most people are only getting a few percent of people clicking on their Adsense units, so that's pretty minimal.
Try the Google SEO forum here for more information on bounce rate. By itself it doesn't mean a whole lot - I have a huge bounce rate on some of my pages, because people come, see what they want, and leave - either via an ad, or a link, or they just go away. But it hasn't hurt either my rankings or my AdSense earnings.
Now if I were Google, I might pay attention to whether or not AFTER the bounce people came back to the search engine and picked another result - because that would indicate that the first choice wasn't a good user experience for them, and they didn't find what they wanted. I'd be more likely to use THAT as a factor than just raw bounce rate (where the user looks at one page and then leaves)