Andres and Guillaume have posted on the Groovy Users list the pointers to many (if not all) the Groovy and Grails sessions of JavaOne 2008... You want to learn more, this is a great opportunity to do it so:
Thanks to all of the authors... I would love to be there watching these session live... This post is the opportunity also to point you to this video from InfoQ of Jason Rudolph doing a very nice introduction to Grails during last year QCon conference...