SEOmoz is extremely vital for small businesses. Without large marketing budgets, these companies need to invest in marketing tools that they will be able to use to take action - that's what SEOmoz allows small business to do. As PII rules and revenue generating tactics change among search engines, social networks, and aggregators shift, it is important to have resources looking for ways to help you succeed in the ever-changing digital landscape.
If you hire an agency to help you with social marketing, SEO, SEM - it is worth reading the resources on SEOmoz. Find out what your agency is telling, if they are smoke screening you (sadly this happens more than we would like to think), and learn the important questions to ask. In my experience, the best questions get the most actionable answers.