Networking sites provide a platform to connect. Different sites appeal to different user base. Sometimes, the user base significantly overlaps. But, the users look for different things on different sites and their preferences change depending on which type of community they are in at the moment even if they are on the same site.
We generally find these sites with either of the dominating flavors - community building or networking. In community sites, people generally have similar things to do and matching interests. Networking sites also help create targeted communities so I am in.
Networking sites help create an understanding that they are here for some purpose. For example LinkedIn, people want to connect with other professionals in their industry. They talk about business leads and expert advice. This is true for Facebook also to some extent. Orkut seems to be a place for fun. Orkut, in my opinion, may not provide much targeted business value.
Companies are using social networking in many ways to make their presence felt. It started with official blogs where employees write about business and technology. Blogs are being used as a platform for informal press releases, creating a discussion forum, creating awareness about future plans etc. Adobe, after acquiring Macromedia, is doing it quite well.
Networking sites can be used by support/marketing teams to make the presence felt in user groups where target segment is already there. Facebook can be a good case for that. People are more comfortable if they find support executives available in the same community they are a part of. They feel more at ease.
Members at LinkedIn often ask open questions on varying topics. Related domain experts provide their opinion and also present themselves as potential solution providers. This could be you if you want to use social networking to promote business. Challenge is to connect to right people in your domain / business.
Open Source communities are contributing a lot to build the future internet. It is increasingly defining the software and internet business. Open Source is helping small organizations and professionals grow at tremendous speed on the net.
Google provides free APIs that developers use for developing applications. They even help create small business solutions for free. To cash on the phenomenon, now everybody is trying to offer something free for the web surfers. Can you think of making some technical expertise available to professionals? That can help you position yourself as right place for the right talent; and for small vendors you will be their default choice when they grow with you.
Just think, how much you can contribute to a community? Then, grow with the community. Choice is always there.