Google's Webmaster Help Center has added some information about those extended descriptions that offer extra links to deeper sections of the website. These results are sometimes seen at the #1 postion of the SERP, and there has been some ongoing question and conjecture about how they are chosen and when they are displayed.

...We only show Sitelinks for results when we think they'll be useful to the user. If the structure of your site doesn't allow our algorithms to find good Sitelinks, or we don't think that the Sitelinks for your site are relevant for the user's query, we won't show them.

At the moment, Sitelinks are completely automated. We're always working to improve our Sitelinks algorithms, and we may incorporate webmaster input in the future...

Google Information on SiteLinks [google.com]

Here are some of our previous discussions on the topic:

1. Google Publishes Information on Sitelinks [webmasterworld.com]

2. Webmaster Tools Shows Sitelinks Information [webmasterworld.com]

3. Site Search Box under Sitelinks [webmasterworld.com]

4. Webmaster Tools Shows Sitelinks - but they're not in the SERPs [webmasterworld.com]

5. Google has Given Me Sitelinks - should I be excited? [webmasterworld.com]

6. Google SERPS - subcategories with site links in the description [webmasterworld.com]

7. Extended description at #1 -- now PLUS a #2 result [webmasterworld.com]

8. Does Google Sitemap help to get "extended listings" [webmasterworld.com]

9. Extended site description - what makes the extra section happen? [webmasterworld.com]

[edited by: tedster at 9:27 pm (utc) on Oct. 11, 2008]