Most small and mid sized businesses are just dipping their toes into blogging. With keyword research and a good analytics package, it's not hard to plan and measure how blogging will impact the bottom and top lines for a business. If it's an ecommerce site, blogging is a no brainer. If you're a b2b company trying to generate leads... again... a no brainer. If you're b2c and people are passionate about your types of products (ie you sell wine not hammers), also a no brainer. If you're a realtor, you should be talking to Real Estate Tomato about how to start a real estate blog... umm... yesterday. (Of course, you shouldn't underestimate what's required to be successful with a blog - no matter who you are or what you sell.)
All that said, social media is still the wild west. There's no best practices. There are very few services that assist business owners in a meaningful way. The only businesses that are taking advantage of social media are big brand name F1000 companies. They have the budgets to deal directly with the big social networks and the budgets to tap the big ad agencies who deal with the big social networks.
Everyone else is sorta left figuring this out themselves. I've been able to successfully generate leads from social media activity. So has the internet marketing company I work for. We teach our clients best practices for the sites that actually drive traffic directly, and support our clients' SEO strategy. We also give them the tools to analyze effectiveness in terms of traffic, leads and soon: sales across their SEO, PPC, blogging, and blogosphere/social media activity. This informs what works and what they should do more of. For example, if Digg reaches your audience, you should learn how to use Digg. If you're trying to reach a younger crowd, join facebook. If you're trying to reach CEOs, start answering questions and endorsing people on LinkedIN.
But, this list could go on and on. How does someone know where to focus their efforts and how do they measure what's working before the leads come in? As this map indicates, you could literally spend all of 2008 registering and learning social media services. There certainly isn't a comprehensive tool within the reach of the average mid sized business to track all the leading indicators of social media success or failure. However, is it really necessary to track the leading indicators? If you have a website that converts visitors into leads and you can successfully generate traffic from social media sources and measure which social media sites send visitors with a high likelihod of converting to a lead... then... I'm left with the conclusion that you should just find yourself a social media advisor. I'm sure that 1 out of 50,000 people are like me (or the guys at Read/Write Web) who spend too much time tracking the social media landscape, who can interpret it and translate it for the average business owner so they know what to do first.
And if in doubt and you don't want to find an advisor, start with LinkedIn. If you're in business, chances are that your best prospects are on there.