As you probably know, social bookmarking as a marketing and backlinking strategy has been around for a few years. There seems to be no decline in their popularity, especially for off page SEO purposes. Still, you really should never neglect or overlook what could be done for the more long-term methods at high PR bookmarking sites. It basically is a matter of your particular business goals and perhaps what appeals to you. Social bookmarking sites generally give you a place to keep bookmarks, for those who are really new to IM. Plus you can tag your bookmarks with your particular keywords, which can help with some SEO, but it tends to be temporary.
Several years ago the more popular bookmark sites made all their links to nofollow which had a huge effect on bookmark rankings. Places like Technorati and Digg, plus a few others were able to dominate the first pages of SERPS in Google due to their high PR status. Who really knows if Google had any influence over those powerful bookmarking sites and the nofollow relational attribute. However it is interesting, and we all know how Google is or can be. Read the rest of this entry