To give you an idea, Pearl-Guide.com is a type of social network. As is Facebook and MySpace.
Social networks do different things. Some, like delicious, collect bookmarks which people can share amongst others who have a similar interest or are just connected through the social network. If someone who is a member of Digg, for example, happens upon a post on PG (which happens about 100 times per day) and likes what the post says, he or she may "digg" it which loads the post onto the Digg network. If other people find it of interest as well they may "digg" it as well, from the Digg network. It can go from there to blogs, RSS feeds, news sites, etc.
If members here use one or more of the networks they can tag specific posts of interest and categorize them in their own way. Sort of like creating a bookmark with IE or safari. The only difference is that the information is stored on the Internet (shared or not) and not on their computer. I do this quite often as I have private (not shared publicly) accounts at my office, on my laptop, and on my home computer. I keep the same bookmarks on each one via social tags, and I only have to tag things once.
This is just a small part of it I know. There is a lot more to it as each of the social networks are different and I only use a couple of them. Our plan is to display the icons and then monitor whether or not they are used. Those that are have an added value to people here. Those that are not used do not. But the only way to really find out whether or not people will use them is to put them on the posts.
I recommend playing around with one. I really like "delicious" personally. Sites that are "tagged" show other "taggers", or other people who have bookmarked them. They are usually categorized within a single subject (like pearls, for example) and their tags lead to articles and pages I may have not seen before. I have found some really great sites and articles that way.
Oh, and yes. Millions of people use these tags, especially the more popular ones. Most blogs have them embedded now as well.
