I am using it on this site in my portfolio section. The intro has thumbnails and then these are not there in the full version. But I do copy the text, so it looks like the thumbnail just was removed…
I was going to write a handy tutorial to this, but Fotis Evangelou beat me to it! His excellent guide is at:
www.webpr.gr/joomla/2006/07/hide-introtext-when-viewing-content.html