McMohan - 3:57 am on Mar 14, 2008 (gmt 0) [edited by: McMohan at 3:57 am (utc) on Mar. 14, 2008]
Perhaps it uses the toolbar data to some extent? Such as the amount of traffic a site gets by direct URL type-in. Searching for the company name in Google also seems to have some influence on whether a site will get sitelinks. These two factors are telling of a company whose name and URL are familiar to a large audience and speaks authority.
[edited by: McMohan at 3:57 am (utc) on Mar. 14, 2008]