In a recent Q&A some of the folk from Google answered some of the hot questions from, well, anyone with them. One of particular interest was that of a site's bounce rate and whether or not it has an impact rankings.

From the information we have at hand, nothing has been 100% confirmed but it is at the very least possible Google may use this as one of their many signals.

Considering Google like sites that please their users, a healthy (low) bounce rate would be a good way to determine if a site fits within the specified criteria. Even so, it isn't the only one used and bounce rates are calculated in a way making them subject to inaccuracy for this purpose.

Regardless of the above you should still keep an eye on your bounce rates, if they are higher than 50% something isn't working. It could be one of many things to, your site is broken somewhere, your branding isn't right, your marketing is off somehow or something similar.

If they are floating around 40% you may still want to take a look and see if and where any improvements can be made. Naturally you want your bounce rate as low as possible, this is an indication people are sticking around and will greatly increase the odds of your site making conversions.