atlrus - 12:57 pm on Apr 3, 2009 (gmt 0)
I see them a lot in the dot com Google. It seems they are limited to just 4 and the difference between them and the "sitelinks" is that you don't have to come at the #1 spot for the mini sitelinks to show.
It looks like they are "given" to the website and will show every time the website shows in the SERPs regardless of position. And it does look like a nice touch.