At it’s most basic definition, social bookmarking is an easy way to say “Hey guys! Look at this cool site I found!” without having to individually message all of your contacts.

This also leaves it open to be a tool to keep up with your friends and family – to see what they’re doing online and what interests them.

Because social bookmark sites keep track of how many times a sites is bookmarked – or “Dugg” – social bookmarks are also tools used to gauge the popularity of articles, sites and blogs.

For instance, upon logging on to Digg, the index shows the most popular recently submitted links. From there, the visitor can see the most popular links in the last 24 hours, 7 says, year et cetera.

Similarly, Technorati‘s front page shows rising stories – though they are divided by whether they are news stories or blog posts (unless you’re logged in; then it shows updates from your favourite blogs as well as when your blogs last pinged – or alerted Technorati of – updates).

Both sites allow visitors to view bookmarks in a variety of categories from business to technology to politics to entertainment to lifestyle and beyond. Furthermore, users can browse by media type such as image or video.

Technorati‘s provisions for blog posts might make it a bit more popular among bloggers as often times, blog posts do not seem to fit within Digg‘s “news story” submission process.

Technorati‘s Blogger Central allows blog owners to “claim” their blogs and submit updates via RSS feeds which publish automatically to a profile page for their blog. From there, others can add the blog to their favourites. Technorati also searches for links to blogs – or “reactions” – which help determine its popularity. Blogger Central also has widgets for use on your desktop, in your browser or on your blog to keep you connected to Technorati all the time.

Digg seems to be a bit more advanced in that it has a friends system, allows comments on submissions and users can send their Diggs/submissions to friends via “shouts.”

However, Digg and Technorati are not the only 2 on the scene.

Del.icio.us is a popular, if much simpler site. Sign up, upload a copy of your bookmarks/favourite from your browser and via plug in or browser, you can add sites to your favourites list. Del.icio.us is big on tags which describe the type of content you’re uploading. Unlike Technorati or Digg, it’s more about traditional bookmarks than news stories or blog posts so pretty much everything feels at place here.

The Del.icio.us homepage shows hot stories and tags. Visitors can view submissions by popularity of recentness.

Upon logging in, visitors see all the bookmarks they have added to Del.icio.us as well as tags. “Your network” shows submissions from friends and “Links for you” are similar to Digg shouts in that your friends can specifically send a recommendation your way. Set up tags you’re interested in and new bookmarks with these tags will show up under “Subscriptions,” similar to Technorati‘s Watchlists.

StumbleUpon is another popular option for social bookmarking; however, that is not its sole purpose. SU is a browser add-on which allows people to recommend sites via categories/tags. Other users can set up a profile and indicate which topics are of interest to them; the stumble upon toolbar will then take the user to a random site based on these tags when. This is known as Stumbling.

Stumble Upon also lets visitors connect with friends to see what they’re browsing, view popular sites, and post to an on-site blog. SU also divides content by media type (videos, images), has a message system and even has groups for those of similar interests. Like Del.icio.us, tags are important in SU.

However, there are many more social bookmarking sites online. Some are general and some are geared toward a specific interest group. Check out Slashdot, Reddit, Newsvine, Bloglines and Yahoo!buzz.