Common Name: imeem
Niche: music - social networking / social media webiste
Slogan: What's on your playlist?
What they say about themselves: "imeem is a social network that enables users to discover, interact and express themselves with media, including music, video and photos, and form connections based on shared tastes and interests."
What I say about imeen: Nice, focused primarily on music with lots of good music. The community aspects include Battles and Pools where members vote on favorite tunes, artists and groups. Clean simple interface and not too much advertising -- if you're into music, imeen is for you.

www.imeen.com
Common Name: Hyves
Niche: Holland's #1 Social Networkng Website
Slogan: Always in touch with your friends.
What they say about themselves: "Holland's most popular website, with over 7 million members and over 2 billion pageviews per month."
What I say about Hyves.net: Well, I'm not from Holland, but the members look like they are having fun. Active user pages with lots of "friending". Videos are their own, (not YouTube). Site has a multi-lingual interface, (mostly european laguages). Main features are personal pages, videos, photos and connections to schools / classmates. The namesake "Hyves" are topical interest groups, for example their World Soccer Hyve with over 350,000 members!

www.hyves.net
Common Name: hi5
Niche: general / social networking website
What they say about themselves: "Find friends in your hometown or other parts of the world. Show off your photos. Listen to music you like. Reconnect with old classmates. Build your own page and express what's important to you."
What I say about hi5: yawn... there's nothing there. The little bit of the site you can see without logging in shows user profiles with one photo or none at all. I search for VERY popular topics like "dogs" or "pets" or "cars" and found a few dozen posts. Is hi5 still in business? If so, why?
http://www.hi5.com
Common Name: Friendster
Niche: adults (18+) - Social Networking Website
What the say about themselves: "Friendster is focused on helping people stay in touch with friends and discover new people and things that are important to them. Online adults, 18 and up, choose Friendster to connect with friends, family, school, social groups, activities and interests."
What I say about Friendster: Yet another genic SMN with Youtube video, photos, and a lot of immature apps to add sparkly things and flashy graphics to your profile. Blatently commercial pages and heavily spammed forum postings. Corporate users create "social advertising pages" mixed in with a lot of childishness and ranting and raving.

www.friendster.com
Common Name: Engage.com
Niche: Social dating
Slogan: "nice to meet you"
What they say about themselves: "Our goal? Make it as easy to meet new people and explore an attraction online as it is to discover someone new at a trusted friend’s party, out in the real world."
What I say about Engage.com: nice idea, you socialize and earn points for uploading photos, posting, making friends, in the end, the more social you are, the more points you get -- the idea being to meet someone online sets Engage apart from the MySpace clones.

www.engage.com