An updated WebmasterWorld thread notes that Google has appeared to add a time stamp value to the last date Google updated your Google Sitelinks. The time stamp can be found by logging into your Google Webmaster Tools, clicking on "Links" and then on "Sitelinks." Here is a picture:
All the screen captures I have from before, including the latest one from December 2007 did not have this time stamp marked on the links. I am not sure how recent this time stamp is, but I think it is a nice enhancement, especially because I often see people ask the question - when did Google last update my Sitelinks.
So, now I know Google last updated this site's Sitelinks two days ago, on the 23rd.
Forum discussion at WebmasterWorld.