Classroom+Uses

How could each of these be used in a classroom setting?

Delicious - online storage of website, that also allows you to share with others and research what others have found under topics of interest.
 * Professional productivity - bookmark pages no matter where you are
 * Research of what others who have tagged a site have found with the subject
 * Create multiple accounts, use for storing class specific websites
 * Keyword searching

 Diigo - allows user to bookmark pages of interest but also annotate and highlight sections on the text for other to see. [|Features video]
 * find information sites for student and annotate / highlight information that is relevant to the subject. Example - http://www.diigo.com/064x5
 * Research what others have found on websites
 * Join online communities with others who have similar interestes

StumbleUpon - random exploration of sites that others have marked as interesting, in subjects that I have marked as an interest.