Diigo is a useful tool that bookmarks and enables sharing of resources. It is a cloud service so nothing is stored on a computer. Diigo accounts are managed with a username/password and a continuum of privacy settings are available. Free accounts are available.
Diigo may be very useful for teaching. Instead of posting announcements or sending emails that with links to resources, just post them right on Diigo. Then, students have one link to manage (your Diigo account link) to find all important class resources. This helps the student tremendously.
My Diigo account is a work in progress.