When you use the tagging features of the major bookmarking sites, you can easily create a list of relevant links for anyone to surf. For instance, if you are wanting to learn about VOLCANOES, you could find and add sites to your bookmarks that deal with volcanoes, but adding an additional tag of "classvolcanoes" or "period1volcanoes." This way, you can click on the unique tag and have one page with a unique web address that you can use in classes, to give your students to explore for homework, or just as an online resource for their research.
Many teachers in the past have spent hours creating "Virtual Field Trips" which not only involve finding relevant links, but also the creation of a web page and directions for using the different sites. With Social Bookmarking, you can save notes along with your tags and label websites with specific information that your students can see, whether it's a description, a direction, or just your reasoning for choosing a particular website. In this way, you can very easily build a specific web listing of the sites you want to visit without the rigomarole of going through the entire Virtual Field Trip process!