http://twitter.com/
This is a “Presence App” which allows members to leave short messages (similar to Facebook feeds) under 140 characters. It does not allow you to make a link in post, but it does link to your profile which could include business information. Purpose is to tell people what you are doing now.
flickr
http://www.flickr.com/
Allows users to store and share photos. Owned by Yahoo. Removes links on submission. Potential to market through profile and commercial images. Hosted images tend to get shared on sites such as MySpace and Facebook. Advertising is available through Yahoo.
http://www.facebook.com
Allows you to reach users through news feeds and applications, as well as walls (guest-books) and direct user to user messaging. Does allow posting HOWEVER it uses a redirect from a Facebook page, so it is not beneficial to SEO. It has its own applications development framework which can access news feeds and other data. To attract interested people towards a page or cause, groups can be created. Allows the creation of business pages. Possible to advertise by age, gender and other user characteristics through an internal advertising program. You can also collect user statistics by subscribing to its business services. Facebook has recently overtaken Bebo in terms of visits.
MySpace
http://www.myspace.com
An older profile pages system like FaceBook. One of the main differences is that MySpace allows users to customize page layouts. It has its own internal advertising program, and allows for the creation of business pages and groups. It also allows linking without nofollow. Oldest and most vulnerable to spam. Allows users to publish images, videos and music. Should be part of the OpenSocial applications development platform from Google. Still maintains a majority market share in the Asia Pacific region.
Bebo
http://www.bebo.com/
Similar to MySpace. Has an open applications framework like Facebook, and allows users to customize pages. Also allows for video hosting and music channels similar to MySpace. Allows advertising using Yahoo. Was recently overtaken by Facebook in terms of traffic
Digg
http://www.digg.com/
Allows users to submit and vote for articles submitted by other uses. Users can also bury articles. Having a high ranking article means a link without nofollow on the front page of a PR8 site plus thousands of visitors. Diggs are tracked by user account. Frequently digg posts are Flickr, Youtube and other social media objects. Allows advertising through Microsoft. Users tend to bury bad posts.
YouTube
http://www.youtube.com/
Allows users to contribute and host videos. Specific interface designed for distributing videos on other sites. Allows posting of links with nofollow. Viral video marketing potential as users can search by views. Owned by Google. Allows for AdSense advertising through Google.
del.icio.us
http://del.icio.us
Social bookmarking site owned by Yahoo. Allows users to store bookmarks and provide them with descriptions and tags. Non-internal links are no-follow, but site contains a hotlist of popular items which appear on the front page. Recently there are reports that Yahoo is taking action to stop bots from other search engines including Google from indexing its content, although I can still find del.icio.us results in Google (punch site:http://del.ico.us into Google search field).
technorati
http://www.technorati.com/
Allows users to post articles into different categories. Users can then comment on articles and add or remove “authority” by voting for them. Allows links without nofollow. Posts with “Authority” appear higher up. Has its own internal advertising system.
orkut
http://www.orkut.com/
This is Google’s social media network. It allows for the creation of groups and should incorporate Open Social. It doesn’t have an advertising program yet.



