I have been using Google Analytics on our company website for several years and it has provided useful information on click thoughts, demographics, referrals etc. Just over month ago Google opened up the beta of Universal Analytics which increases the referrers to include social media, mobile (web and apps), advertising (Google and non-Google), and even email marketing and links within PDF documents.
There are many social media marketing tools out there but this seems to be the only one that follows that traffic all of the way back to your website and can measure conversion. It might not replace your other social tools, but it you are also running a website you need a tool that watch the entire click steam of your customers.
There are free and premium versions of the product but the free product is great for anyone who has a website in addition to their social media accounts. The ability see which social networks are driving traffic to your site can help create more effective mobile strategies.
To check out the features visit https://www.google.com/intl/en_ALL/analytics/features/index.html
The Analytics blog also shows the power of the new features. http://analytics.blogspot.com/