Websites such as Digg, Delicious, StumbleUpon, and Reddit list URLs or bookmarks that have been submitted by Web users all over the world. The idea is that if somebody comes across an article or blog post they like, they can submit it as a bookmark and, in doing so, recommend it to other people. The more people who bookmark a particular blog post or article, the higher up the listing pages it will appear. Having one of your posts appear on the front page of Digg or one of the other social bookmarking sites, could send an avalanche of traffic to your blog.
Google has recently launched a bookmarking service called Google +1. By clicking on the Google +1 button, which may appear on a web page or in Google search results, you are giving that web page your seal of approval or recommendation. Your +1's are...