This is a social networking site with a slight twist. Instead of just being able to "bookmark" and share websites, Diigo allows users to search tagged sites and even leave "sticky notes" on the site. Certainly more useful than just bookmarking if you ask me. I think social networking sites are useful but it can only be used as an advertising platform and nothing more. But if you have the ability to search information on tagged sites, it would be so much more. Have you ever found a website which contains so very important information, only to find out that you can't remember which part of the site you found the information. Diigo features allow you to search and find the information easily through all your tagged sites. It is like a website manager of your important information. Premium account holders can even search cached copies (cached as in cached in Diigo's database), so you will never lose information again. They have apps for iPad, iPhone and even Android. Pretty nifty if you ask me.