Share 'Social Bookmarking'

Teachers from the Trenches My students are learning about and beginning to set up their own Social Bookmarking site like del.icio.us or Portaportal, etc. If you have an opinion about social bookmarking or one to share, we would really appreciate taking advantage of your resources. I have two, a del.icio.us site, that I basically use it for on the fly bookmarking then I move sites to my Portap...