Occasionally, a webmaster panics to see that his listing in the SERPs has suddenly changed to only show the url, with no title or snippet. This can be the sign of a possible penalty, however, more often than not, it is a problem that will correct itself over time. Google calls these listings Partially Indexed Pages (as opposed to Fully Indexed Pages), which indicates that they know about your page, but have not yet fully crawled the page. Once it gets fully crawled, it will show a title and snippet. This can sometimes happen if your site was down while Google was attempting to crawl your page. For more info, you can go to http://www.google.com/webmasters/3.html.