You might be using these for the networking opportunities. And, you may use the connections and dialogue in work applications.
For those of you whose responsibilities -- either directly or indirectly -- involve organic Web site optimization, let's look at how you can get SEO benefits out of social networking.
When it comes to social media and social media marketing, it's important that you reserve your brand's name (or your company name or personal name) on the more popular social networking Web sites. These include sites like Twitter, StumbleUpon, Mixx, Digg, reddit, Facebook, LinkedIn, and others like MySpace and YouTube. You don't necessarily have to be active on the Web sites; however, it's important to reserve your name and fill out your profile on those Web sites.
Typically, many of those sites allow you to put your site's URL on your profile page. Some sites, like LinkedIn, allow you to add more than one link, so take advantage of those links. Also, look at User Name Check to see where your brand is and isn't registered, and claim the ones you can. If you're overly enthusiastic, take a look at Wikipedia's social media list.
Linking over to a few of your more important profiles is fine. Telling your Web site visitors to "follow you" on a certain social networking Web site is OK, too. After all, Matt Cutts of Google recommends that you follow him on Twitter and FriendFeed.
However, keep in mind that real people will follow those links (this isn't just for SEO purposes), so link to a social media profile that you update regularly, not once every six months