How Many Social Networks Should You Belong to?

With as many as 250,000 social media type sites up and running, and with social networking sites being such effective places to network and promote your business, I often wonder how many social networks I should belong to?
I currently belong to six social media type sites; LinkedIn, Facebook, Twitter, Delicious, Blog Catalog and Technorati; and I use each of them differently.
I use LinkedIn solely for my personal business contacts.
Facebook being more personal, I use to connect with friends, family, and more personal contacts I have made through networking.
I use Twitter solely for networking and website promotion.
Blog Catalog and Technorati I use to connect with other bloggers and for blog promotion; although I don’t actively keep up my Technorati profile.
And last I use Delicious to bookmark my pages and posts from my blog, hence creating back-links and greater visibility.
With this being said, I keep hearing all the hype about StumbleUpon, Digg, MySpace and YouTube.
Should I create accounts with these sites too?
I am a firm believer in quality over quantity, and right now if I were to add another social network into the mix I wouldn’t be able to sufficiently keep up with it, which in turn would decrease my online value.
Right now I am able personally answer emails and messages from these networks, which helps me to build stronger relationships and connections. And most importantly, I am able to write frequent blog posts.
For companies to create a solid online presence by utilizing ten to twenty different social media platforms they need someone to solely focus on the task at hand, such as a social media marketer or they need to delegate the various networks out to numerous employees.
Here are a few questions to consider when deciding how many and which social networks to belong to:
1. How much time do you have to invest in each network?
2. What are your goals for social networking?
3. How will you utilize each site and which niche social networks best fit your needs?
Once you have decided on your social networking strategy, you can save some time by creating a hub for your social networks using one of the services below:
Google Profiles
Zoho