Building a successful social media marketing campaign for a small business is about choosing 3 or 4 and sticking with them. If you are trying to update to 20+ social media services than you are spreading yourself too thin!
My suggestion for the small businesses looking to seo your website and build a social media presence is to stick with the big ones. Twitter, Facebook, YouTube, Flickr, and I really like StumbleUpon for sharing.
Focus your attention on those, build a plan for each that works together with your website and business goals, then execute your social media marketing plan.
To make things easy to manage, I highly suggest the service Postling. What Postling does is connects all your social media, blogs, and other accounts together (even LinkedIn and FaceBook!) so you can easily manage them all from one dashboard. I personally use it for myself and many clients and have found it dramatically reduces my workflow when trying to build links and get the word out.
I've arranged a discount for clients and my blog readers: 50% off Postling Coupon.