I have to admit this is one area that I never really got into, and continue to struggle to find relevant to the way I do things. The 23 Things Kansas post about Tagging and Social Bookmarks highlights websites like Delicious.com, Diigo, and Blinklist. I created a Delicious account back in 2006 (back when it was still del.icio.us). I only created a handful of links, and also imported all of my Google bookmarks. Diigo I only recently discovered, and actually do enjoy using it for the purpose of researching a topic (i.e., for a school paper, etc.). Neither one am I very faithful about updating or keeping current. Blinklist is highly susceptible to corruption through spamming, so I avoid it like the plague.
For the purpose of bookmarking, I mostly use Google Bookmarks, which are available to me no matter which browser or computer I am using. Even more than that, I have also recently begun to rely heavily on Google’s ability to “star” search results. This is also great for aiding your use of Google search on the go: you can search for something using your desktop (say, a restaurant’s page on urbanspoon), star the search result in your browser, and then when you repeat the search on your mobile browser, your starred result is right at the top. When you combine starring search results with Google’s Web History features, finding sites you’ve already visited and found interesting is incredibly easy.
There are times when I do indeed need to harness the power of social bookmarking: primarily when I have exhausted my Google search abilities with no good results. Repeating the same or similar search in Delicious can show me which sites other people have bookmarked with tags similar to my search terms. This is also great when searching for broad topics and need a quick way to narrow your thoughts down to a more specific topic.